GIFT  OF 
Mr*.   H.  T. 


PRACTICAL  DIRECTIONS 


-FOR- 


AND 


FIELD-MAGNET  WINDING. 


BY    EDWfllJD 


AUTHOR  OF 

Everybody's  Hand-Book  of  Electricity, 

How  to  make  Electric  Batteries  at  Home, 
Experimental   Electricity, 

Dynamos  and  Electric  Motors, 

Electricity  and  its  Recent  Applications, 

A  Practical  Treatise  on  Electro-Plating,  etc. 


ILLUSTRATED. 


CONTAINING   WORKING    DIRECTIONS 

FOR  WINDING   DYNAMOS    AND    MOTORS,    WITH    ADDITIONAL    DESCRIPTIONS    OF    SOME 

APPARATUS  MADE  BY  THE  SEVERAL  LEADING  ELECTRIC    COMPANIES 

IN  THE  UNITED   STATES. 


Itynn,  JVlass.: 

BUBIEJ*   PUBLtlSHH^G   CO|WPflJ4Y. 
1892. 


VA  -T. 


COPYRIGHTED  BY 

BUBIER    PUBLISHING    COMPANY. 
1892. 


Press  of  G.    H.  &  W.  A.    Nichols,    Lynn,    Mass. 


PREFACE. 


THE  winding  of  a  dynamo  or  motor  is  a  matter  of 
some  difficulty  (as  all  students  of  Electricity  have 
discovered),  hence  many  attempts  otherwise  success- 
ful, have  ended  here  in  failure  and  discouragement. 
The  importance  then  of  knowing  how  to  wind  a 
machine  properly,  can  be  seen  at  once.  . 

The  standard  works  on  Electricity  contain  very 
little  practical  information  on  this  subject.  The  reason 
for  this  lack  of  information  probably  is  the  fact  that 
the  art  of  winding  was  to  a  great  extent  theoretical, 
until  a  very  recent  date.  At  present,  although  not 
absolutely  perfect,  electrical  knowledge  has  reached  a 
more  scientific  basis.  By  following  certain  rules,  one 
may  wind  a  machine  to  obtain  almost  any  result 
desired. 

In  this  treatise  theories  have  not  been  deeply 
entered  into,  the  information  being  more  of  a  practical 
character.  It  is  thus  adapted  to  the  use  of  beginners 
and  to  the  more  advanced  student.  Illustrations  have 
been  used  wherever  necessary  to  make  the  text  clear 
to  the  mind  of  the  reader. 

EDWARD  TREVERT. 

LYNN,  MASS.,  Feb.  10,  1892. 


46450? 


CONTENTS. 


INTRODUCTION. 

CHAPTER  i.— The  Armature  in  Theory. 

CHAPTER  2.— Forms  of  Armatures. 

CHAPTER  3. — Drum  Winding. 

CHAPTER  4.— Field  Winding. 

CHAPTER  5.— Field  Formulae. 

CHAPTER  6. — General  Methods  of  Winding. 

CHAPTER  7. — Field  Winding— concluded. 

CHAPTER  8. — Dynamos. 

CHAPTER  9.— Motors. 


Armature  and  Field-Magnet  Winding, 


INTRODUCTION. 

ALL  magnets  are  surrounded  by  what  is  known 
as  a  field  of  force.  The  familiar  experiments  with 
the  magnet  and  iron  filings  give  us  some  notion  of 
the  character  of  this  field,  for  the  filings  always 
adjust  themselves  along  certain  lines,  generally 
curves,  depending  for  their  shape  upon  the  form  of 
the  magnet. 

The  region  surrounding  the  magnet  is  conceived 
as  being  penetrated  by  "  lines  of  force,"  which 
radiate  from  the  poles  and  are  parallel  to  the  lines 
of  iron  filings.  They  emerge  from  the  magnet 
something  like  the  bristles  of  a  brush,  and  always 
form  closed  curves,  that  is,  they  always  return  by 
longer  or  shorter  routes  to  the  body  of  the  magnet 
and  through  it  to  the  starting  point.  It  is  for  this 
reason  that  it  is  impossible  to  make  a  unipolar 
magnet.  Every  magnet  must  have  two  poles,  a 
north  and  south. 

These  lines  do  not  pass  with  equal  facility 
through  all  substances.  Most  bodies  offer  a  high 


resistance  to  them,  but  iron,  steel,  nickel,  and  one 
or  two  others  to  a  less  degree,  are  good  "magnetic 
conductors."  Magnetism  always  follows  the  path 
of  least  resistance,  and  with  a  given  magnetizing 
force  the  intensity  of  the  resulting  magnetism  is 
enormously  increased  by  the  presence  of  iron.  It 
is  for  this  reason  that  we  use  iron  in  the  fields  of 
our  dynamos  and  motors  and  we  shall  see  later 
that  it  is  of  the  highest  importance  that  the 
" magnetic  circuit"  or  path  over  which  the  mag- 
netic force  passes  should  have  a  large  cross  section 
and  a  low  resistance. 

Whenever  a  conductor  of  electricity  is  passed 
through  the  field  of  force  surrounding  a  magnet,  at 
right  angles  to  the  lines,  an  electromotive  force  is 
set  up  in  it,  depending  upon  the  length  of  the 
conductor,  the  speed  at  which  it  moves,  and  the 
intensity  of  the  field.  This  fact  is  the  one  utilized 
in  the  construction  of  dynamos,  and  forms  the 
basis  of  our  calculations,  for,  knowing  the  strength 
of  the  field  magnets,  the  length  of  the  wire  on  the 
armature,  and  the  speed  at  which  it  revolves,  we 
have  all  the  data  necessary  to  calculate  our  electro- 
motive force. 


ARMATURE   AND    FIELD-MAGNET  WINDING. 


CHAPTER    I. 

THE     ARMATURE      IN     THEORY. 

IN  making  our  calculations  we  designate  the 
strength  of  the  field  by  the  "number  of  lines  of 
force  "  for  a  given  sectional  area.  In  speaking  of 
lines  of  force  the  reader  must  not  be  led  into  the 
idea  that  these  lines  have  any  real  existence. 
They  simply  form  a  convenient  symbol  for  a  state 
of  affairs  which  nobody  understands  very  clearly 
at  present,  but  which  must  be  dealt  with  in  some 
manner  in  this  kind  of  work.  If  we  take  a  con- 
ductor and  move  it  so  as  to  cut  across  the  field  of 
force  at  right  angles  to  it,  we  get  an  electromotive 
force  proportional  to  the  speed  of  the  conductor 
and  the  number  of  lines  of  force  it  cuts,  or 

s=s-i 

Where  E=  the  E.  M.  F.,  5=  the  speed,  and  / 
the  number  of  lines  of  force. 

Suppose  this  conductor  is  on  the  periphery  of 
an  armature,  /the  total  number  of  lines  of  force 
passing  through  the  armature  from  one  pole  to  the 
other  and  n  the  number  of  revolutions  of  the 
armature  per  minute.  Then  it  can  easily  be  shown 


10  ARMATUKE    AND   FIELD-MAGNET   WINDING. 

that  the  average  E.  M.  F.  generated  in  this  con- 
ductor during  a  revolution  is 

E=2/£ 

60 

To  get  the  E.  M.  F.  for  a  coil  of  wire  instead  of 
a  single  conductor  we  multiply  the  second  term  of 
our  formula  by  the  number  of  wires  in  this  coil 
upon  the  external  surface  of  the  armature  and 
calling  /  this  number  we  would  have 

E=2lt£ 

4 /  would  of  course  be  equal  to  the  number  of 
times  in  a  Gramme  ring  coil  and  double  the  number 
of  times  in  a  drum  armature  coil.  Then  suppose 
we  have  a  number  of  coils  in  series.  The  E.  M. 
F.  for  the  whole  of  them  would  clearly  be  this 
number  multiplied  into  the  second  term  of  the 
above  and  letting  N  stand  for  this  number  of  coils 
we  get 

E=2ltN£ 

As  closed  coil  armatures  are  ordinarily  con- 
nected, they  have  half  the  wire  on  them  in  series 
and  the  two  halves  in  parallel,  so  that  the  E.  M.  F. 
they  produce  is  one-half  that  which  would  be  given 
if  the  entire  number  of  external  wires  (=  N  t)  were 
in  series.  Consequently,  if  we  take  Nt  in  such  a 
case  to  represent  the  entire  number  of  external 
wires,  we  should  get  for  the  E.  M.  F. 


ARMATUKE   AND   FIELD-MAGNET   WINDING. 


11 


The  simplest  form  of  armature  is  the  shuttle 
armature,  devised  by  Siemens.  It  consists  of  a 
single  coil  of  wire  wound  lengthwise  upon  an  iron 
"  shuttle."  (See  Fig.  2,  3,  4,  5.) 

When  this  is  revolved  between  the  poles  of  a 
magnet  a  current  is  set  up  in  the  wire,  the  direc- 


FlG.    I. 


tion  of  which  may  be  determined  by  the  following 
"rule  of  thumb."  Spread  out  the  thumb  and  first 
two  fingers  of  the  right  hand  in  such  a  way  that 
each  will  be  at  right  angles  to  the  other  two.  (See 
Fig.  i.) 


12  ARMATURE  AND  FIELD-MAGNET  WINDING. 


FlG.    2. 


FIG.  3. 


FIG.  4, 


FIG.  5. 


ABMATUKE   AND    FIELD-MAGNET  WINDING. 


13 


Then  if  the  thumb  be  pointed  in  the  direction 
of  motion  of  the  wire,  and  the  forefinger  in  the 
direction  of  the  lines  of  force  (that  is,  from  the 
north  to  the  south  pole  of  the  magnet),  the  middle 
finger  will  be  pointing  in  the  direction  of  the  cur- 
rent. 

It  will  be  seen  that  by  applying  this  rule  to  the 
coil  just  spoken  of  we  find  that  the  current  in  the 


FIG.  6. 

wire  will  reverse  at  each  half  revolution,  and  that 
if  we  desire  the  current  in  the  external  circuit  to 
be  in  one  direction  we  must  place  what  is  known 
as  a  commutator  at  the  point  where  the  current  is 
led  from  the  armature.  The  commutator  in  this 


14  ARMATURE   AND    FIELD-MAGNET  WINDING. 

case  will  consist  of  two  halves  of  a  metallic  cylin- 
der attached  to  the  armature  shaft  but  insulated 
from  it  and  each  other.  The  ends  of  the  coil  are 
fastened  one  to  each  half  of  the  cylinder  and  the 
brushes  or  collectors  which  lead  off  the  current 
rub  against  them.  (See  Fig.  6.) 

Then  when  the  armature  is  in  the  position 
shown,  the  current  in  the  external  circuit  will  flow 
as  indicated  by  the  arrow,  and  when  the  armature 
has  made  half  a  complete  revolution  its  current 
will  be  reversed,  but  at  the  same  time  its  connec- 
tion with  the  external  circuit  is  reversed  by  the 
commutator,  and  the  current  still  flows  there  in 
the  same  way. 

When  the  armature  has  made  a  quarter  revolu- 
tion or  stands  at  right  angles  to  its  present  posi- 
tion, the  brushes  will  touch  both  segments  of  the 
commutator,  and  the  coil  is  short  circuited,  but  at 
the  same  time  it  will  be  seen  that  the  wires  of  the 
coil  are  not  moving  across  the  lines  of  force,  but 
parallel  to  them,  and  that  they  are  therefore  genera- 
ting no  E.  M.  F.,  so  there  is  no  harm  done,  that  is, 
there  would  be  none  if  the  above  statements  were 
accurately  true.  Practically  if  the  coil  has  any 
breadth  it  cannot  be  moving  parallel  to  the  lines 
of  force  at  every  point  at  the  same  instant,  and  a 
sufficient  current  may  be  generated  during  this 
period  to  cause  a  spark  to  form  when  the  short  cir- 
cuit, caused  by  the  brushes  passing  from  one 


ARMATURE   AND   FIELD-MAGNET  WINDING.  15 

segment  to  the  next,  is  broken.  In  well  designed 
machines,  this  can  be  avoided  by  attention  to  the 
shape  of  the  pole  pieces  of  the  fields,  that  is  by  so 
making  them  that  few,  if  any,  lines  of  force  are 
cut  by  the  coils  when  short-circuited. 

The  current  given  by  the  above  arrangement 
while  it  flows  in  but  one  direction  is  nevertheless 
an  intermittent  one,  varying  from  its  maximum, 


FIG.  7. 

when  the  coil  is  horizontal  to  nothing,  when  it  is 
vertical  and  short-circuited.  If  we  wind  another 
coil  on  the  armature  with  its  plane  at  right  angles 
to  the  first,  we  shall  evidently  lessen  this  tendency, 
for  when  one  coil  is  in  its  idle  position,  the  other 
will  be  doing  its  best  work  and  vice  versa,  but 


16  ARMATURE   AND   FIELD-MAGNET   WINDING. 

there  would  still  be  a  jog  in  the  current  strength, 
though  to  a  much  smaller  degree. 

Three  coils  would  evidently  be  a  step  further  in 
the  right  direction,  and  in  fact,  the  greater  the 
number  of  coils  we  use,  and  of  course  the  greater 
the  number  of  commutator  segments,  the  nearer 
we  come  to  having  a  smooth  current.  The  num- 
ber is  limited  by  the  difficulty  of  construction 
which  increases  with  each  additional  commutator 
segment. 

In  the  usual  construction  of  the  closed  coil 
armatures  the  end  of  one  coil  is  connected  to  the 
beginning  of  its  next  neighbor,  and  a  wire  is  taken 
from  this  junction  to  a  commutator  bar,  and  there 
must  therefore  be  as  many  commutator  segments 
as  coils.  This  arrangement  is  best  shown  on  a 
Gramme  ring,  but  the  principle  is  the  same  for 
any  style  of  armature.  (See  Fig.  7.) 

In  the  sketch  showing  this  arrangement  it  is 
seen  that  the  current  in  the  armature  is  flowing  in 
the  opposite  direction  in  the  two  halves  made  by 
the  line  A  B.  In  each  case,  it  flows  from  B  to  A, 
and  therefore  if  brushes  be  placed  against  the  com- 
mutator on  the  line  A  B  they  will  be  in  the  proper 
position  to  take  the  current.  In  an  open  coil  arma- 
ture, that  is,  one  in  which  each  coil  is  by  itself  and 
has  no  connection  with  the  others,  the  brushes 
must  be  on  a  line  at  right  angles  to  A  B,  or  so 
that  they  can  take  off  the  current  when  the  coil  is 
generating  the  highest  E.  M.  F. 


AKMATURE    AND   FIELD-MAGNET  WINDING.  17 


CHAPTER   II. 

FORMS     OF     ARMATURES. 

THE  two  forms  of  armature  most  commonly  met 
with  in  practice  are  the  Gramme  ring  and  drum. 
Each  has  its  special  advantages,  and  in  choosing 
either  we  must  be  guided  largely  by  the  conditions 
governing  the  construction  and  running  of  a  ma- 
chine. 

The  Gramme  ring  armature  consists  of  a  ring  or 
hollow  cylinder  of  iron,  upon  which  the  wire  is 
wound.  Instead  of  going  completely  around  the 
outside  of  the  armature,  each  turn  of  wire  goes 
through  the  opening  in  the  middle  and  thence 
back  to  the  outer  surface  again.  On  an  armature 
of  this  description  each  coil  is  wound  by  itself  and 
is  not  overlapped  by  any  of  the  others,  conse- 
quently if  repairs  are  necessary  at  any  time  it  is 
easy  to  get  at  the  particular  coil  where  the  fault 
is  without  disturbing  the  others,  and  this  is  often 
an  important  point  where  the  armature  is  wound 
with  a  large  number  of  .turns  of  fine  wire.  The 
coils  being  each  one  open  to  the  air  makes  it  bet- 
ter, too,  for  getting  rid  of  the  heat  generated  in 


18  ARMATURE   AND   FIELD-MAGNET  WINDING. 

wire  and  core.  On  the  other  hand  the  wire  which 
passes  through  the  middle  of  the  armature  is 
"dead"  so  far  as  exciting  E.  M.  F.  is  concerned 
and  it  not  only  does  not  help  but  adds  a  wasteful 
resistance. 

Then  a  ring  armature  is  much  more  difficult  to 
wind,  as  the  wire  must  be  passed  through  the 
middle  for  each  turn.  The  cross  section  of  the 
armature  core  is  also  necessarily  smaller  than 
for  a  drum  armature  of  the  same  dimensions 
and  therefore  its  magnetic  resistance  is  greater. 
In  a  general  way  we  may  say  that  the  ring  arma- 
ture is  better  adapted  for  machines  giving  constant 
current  and  high  potential  and  that  the  drum 
armatures  are  the  proper  ones  to  use  for  constant 
potentials  and  large  currents.  The  core  of  the 
ring  armature  is  made  in  several  ways.  It 
should  never.be  a  solid  piece  on  account  of  the 
eddy  currents  which  would  be  generated  in  it,  and 
cause  it  to  heat.  It  might  be  made  of  a  flat  ribbon 
of  sheet  iron  wound  up  to  make  a  cylinder,  but 
this  would  have,  to  a  smaller  degree,  the  same 
objection  as  the  solid  core.  It  is  frequently  made 
of  iron  wire  wound  in  a  former  of  wood  and  shel- 
laced and  bound  with  tape  to  make  it  keep  its 
shape.  This  method  has  many  advantages;  it  is 
cheaply  and  easily  done  and  gives  good  results  and 
unless  one  has  special  facilities  for  doing  the  work 
is  probably  the  best. 


ARMATURE    AND   FIELD-MAGNET   WINDING.  19 

A  core  of  this  sort,  however,  is  slightly  inferior 
considered  as  a  magnetic  conductor  to  one  made 
of  disks  or  flat  rings  of  sheet  iron.  Magnetism 
always  shows  a  preference  for  running  along  the 
grain  of  the  iron,  and  it  would  have  more  difficulty 
in  getting  out  of  the  centre  of  a  core  made  of  wire 
where  it  would  have  to  go  at  right  angles  to  the 
grain  and  besides  have  numerous  air  gaps  to  leap 
across  than  it  would  to  get  out  of  a  similar  core 
made  up  of  disks.  (See  Fig.  8.) 


FIG.  8. 

If  a  core  made  of  rings  cut  from  sheet  iron  is 
used,  some  means  must  be  used  to  hold  them  to- 
gether. This  may  be  done  by  a  bolt  or  screw 
through  them  from  end  to  end,  or  they  may  be 
held  by  the  " spider"  by  which  they  are  attached 
to  the  armature  shaft.  (See  Fig.  9.) 


20 


ARMATUKE    AND    FIELD-MAGNET   WINDING. 


There  is  no  need  of  paper  or  any  other  insula- 
tion between  the  disks.  The  black  oxide  of  iron 
on  the  surface  is  sufficient,  the  danger  from  heat- 
ing not  being  so  much  from  the  small  currents  in 
the  disks  jumping  across  from  one  to  the  other,  as 
from  the  lines  of  magnetic  force  going  through 
the  armature  slantingly.  One  prominent  inventor 
even  goes  so  far  as  not  only  to  discard  the  paper 
insulation  but  to  replace  it  at  intervals  with  disks  of 
zinc,  and  claims  that  his  armatures  run  much  cooler. 


FIG.  Q. 


Another  point  which  should  be  brought  out  in 
this  connection  is  that  the  armature  core  should 
be  the  same  length  that  the  pole  pieces  are  wide, 
in  order  that  the  lines  of  force  as  stated  above  may 
go  straight  from  one  pole  to  the  other. 

In  regard  to  the  necessity  for  some  means  of 
holding  the  armature  coils  in  place  there  is  a 
diversity  of  opinion.  Some  builders  wind  their 


AKMATUKE   AND    FIELD-MAGNET  WINDING. 


21 


coils  upon  a  smooth  core  and  trust  to  friction  and 
good  luck  to  hold  them  where  they  are  placed. 
The  author,  however,  believes  that  there  is  no  use 
in  taking  needless  risks  in  a  matter  of  this  sort 
where  slight  additional  precaution  may  be  the 
saving  of  an  expensive  piece  of  repairing.  The 
necessity  is  perhaps  not  so  great  in  the  case  of 
the  Gramme  ring  as  the  drum  armature,  but  there 
is  no  harm  in  using  it  in  either  case. 


FIG.  10. 


The  strain  on  these  coils  is  of  course  the  resist- 
ance against  which  the  armature  must  be  turned 
and  the  effect  is  very  much  the  same  as  if  a  brake 
were  applied  to  the  surface  of  the  armature  to  pre- 
vent its  rotation.  The  method  generally  em- 
ployed to  prevent  the  coils  from  slipping  is  to  bore 


22  ARMATURE    AND   FIELD-MAGNET   WINDING. 

holes  in  the  external  surface  of  the  armature  close 
to  the  ends  between  the  coils,  and  drive  pegs 
either  of  wood  or  iron  into  them  ;  if  the  latter  they 
must  of  course  be  carefully  insulated.  (See  Fig.  10.) 
Sometimes  the  ends  are  sawed  across  and 


FIG.  ii. 


wedges   of   hard    wood  driven    in,    as   in    Figure 

11,  and  sometimes  these  wooden  wedges  extend 
the  whole  length  of  the  armature,   as  in  Figure 

12.  Perhaps    the    best,    but   at    the  same  time 


FIG.  12. 


most  expensive  way,  is  to  make  the  disks  which 
form  the  core  of  the  armature  like  a  toothed  wheel. 
(See  Fig.  13.) 

When  these  are  put  together  to  form  the  core 


ARMATURE   AND   FIELD-MAGNET   WINDING.  23 

the  projections  will  make  ribs,  running  the  length 
of  the  armature,  between  which  are  channels  in 
which  the  wire  may  be  wound.  This  not  only 
gives  a  solid  construction,  but  also  has  the  advan- 
tage of  reducing  the  magnetic  resistance  of  the  air 
space.  The  core  of  the  armature  must  always  be 
carefully  insulated  by  two  or  three  layers  of  wrap- 
ping paper  stuck  on  with  shellac.  On  larger  arma- 
tures a  layer  of  canvas  is  advisable  between  the 
papers  to  lessen  the  liability  to  breaking  through 
on  corners  and  sharp  edges. 


FIG.  13. 

The  winding  of  a  Gramme  ring  is  not  a  very 
easy  thing  to  do,  since  the  wire  must  be  passed 
through  the  centre  of  the  armature  for  every  turn 
on  the  coil.  You  may  either  do  this  with  as  large 
a  bundle  of  wire  as  you  can  get  through  the  open- 
ing, and  run  the  risk  of  its  tangling,  or  use  shorter 
pieces  and  make  a  number  of  joints. 


24  ARMATUKE   AND    FIELD-MAGNET  WINDING. 

Decide  upon  how  many  coils  you  are  going  to 
have,  and  lay  out  the  ends  of  the  armature  in  this 
number  of  divisions.  If  you  are  going  to  use  pegs 
to  hold  your  coils  in  place,  put  them  in  at  these 
division  marks  and  they  will  serve  as  guides  for 
winding.  You  should  certainly  have  something 
to  guide  you,  so  if  you  do  not  have  the  pegs,  clamp 
on  two  strips  of  wood  the  length  of  the  armature 
core  and  as  far  apart  as  your  coil  is  to  be  wide. 
Then  when  it  is  wound  remove  them  and  proceed 
"in  the  same  way  for  the  next  coil.  Begin  at  any 
one  of  the  divisions  to  wind.  It  does  not  matter 
which  way  you  wind  so  long  as  you  follow  the 
same  direction  in  each  coil.  Leave  a  few  inches 
of  your  starting  wire  hanging  loose.  Shellac  every 
layer  when  you  have  completed  it,  and  when  you 
have  the  required  depth  of  wire,  do  not  cut  it 
off  but  throw  out  a  loop,  and  continue  winding 
with  the  same  wire  and  in  the  same  direction  on 
the  next  coil.  Of  course  these  loops  must  all  be 
at  the  same  end  of  the  armature,  viz.,  at  the  com- 
mutator end. 

Continue  winding  and  throwing  out  loops  be- 
tween each  coil  until  you  have  occupied  all  the 
spaces,  and  when  you  have  finished  the  last  coil 
leave  a  few  inches  of  wire  hanging  free,  and  twist 
it  together  with  the  starting  wire  of  the  first  coil. 
If  the  coils  come  close  together  on  the  inside  of 
the  armature,  and  if  they  are  in  danger  of  touch- 
ing they  should  be  insulated  carefully. 


AKMAT17KK    AND   FIELD-MAGNET   WINDING.  25 

Joints  in  the  wire  should  always  be  soldered. 
If  the  wire  is  small  the  ends  can  be  compactly 
twisted  together,  and  the  place  where  this  is  done 
should  be  where  the  increased  thickness  will  not 
make  a  lump  in  the  winding  which  will  be  un- 
sightly or  in  danger  of  touching  the  pole  pieces. 


FIG.  14. 

Large  wires  are  not  so  likely  to  need  joining 
since  the  coils  made  by  them  are  generally  short, 
and  you  can  usually  arrange  it  so  that  the  break 
will  come  between  two  coils.  Should  it  be  neces- 
sary, however,  to  make  a  junction  in  a  coil,  and 


26 


ARMATURE   AND   FIELD-MAGNET  WINDING. 


the  wire  is  large  enough  to  make  a  large  swell  if 
twisted  together,  bevel  off  the  two  ends  and  bind 
them  together  with  fine  wire  and  solder,  being 
careful  to  get  the  wire  hot  enough  to  cause  the 
solder  to  penetrate  everywhere.  (See  Fig.  15.) 

Sometimes  a  sleeve  of  thin  copper  is  made,  into 
which  the  ends  may  be  slipped  and  soldered,  but 
the  author  prefers  the  binding  wire  method  as 
being  the  surest. 


FIG.  15. 

The  joint  must  be  wrapped  in  white  tape,  after 
having  been  washed  in  alcohol  to  remove  the  sol- 
dering acid  which  would  in  time  destroy  the  insu- 
lation. After  the  armature  is  wound  it  should 
be  put  into  a  drying  oven  of  some  sort  to  dry  it 
out,  for  the  shellac  when  wet  makes  a  very  noticea- 
ble reduction  in  the  resistance  of  the  armature. 
An  oven  heated  by  steam  is  the  safest,  as  it  pre- 
vents the  armature  from  getting  hot  enough  to 


ARMATURE   AND   FIELD-MAGNET   WINDING.  27 

burn  or  char  the  insulation.  The  time  it  is  to 
remain  in  the  oven  will  depend  of  course  upon  the 
size  of  the  armature,  and  the  thickness  of  the 
wire  upon  it,  and  will  vary  from  two  to  twelve 
hours.  The  armature  is  attached  to  the  shaft  in 
various  ways.  In  the  larger  machines  it  is  gener- 
ally done  by  means  of  a  spider,  as  referred  to 
above  in  speaking  of  the  core.  This  is  a  hub  with 
three  or  four  spokes  reaching  out  and  holding  the 
core  by  means  of  channels  or  key-ways  cut  in  the 
inside  of  the  core  to  receive  the  spokes.  In  small 
machines  it  will  often  be  sufficient  to  drive  wooden 
cones  into  each  end  of  the  opening  in  the  arma- 
ture and  pass  the  shaft  through  them.  Suitable 
precautions  must  be  taken  to  prevent  the  cones 
from  abrading  the  insulation  on  the  wires  they 
touch,  by  protecting  them  with  canvas.  The  shaft 
must  be  in  the  exact  centre  of  the  armature, 
since  it  must  run  as  closely  as  possible  to  the  pole 
pieces. 

The  last  operation  to  the  armature  itself  is  to 
put  on  the  binding  wire.  This  is  to  prevent  the 
wires  from  flying  out  when  run  at  a  high  speed. 
The  number  of  bands  you  put  on  will  depend  upon 
the  length  of  the  armature,  a  small  one  needing 
only  one,  and  a  large  one  three  or  four.  Wrap  a 
strip  of  shellaced  paper  and  canvas  around  the 
armature  where  you  have  decided  to  put  your  bind- 
ing wires,  and  then  using  fine  brass  wire,  wind  on 


28  ARMATURE    AND   FIELD-MAGNET   WINDING. 

a  number  of  turns,  till  you  have  a  band  from 
3^  to  y?  an  inch  wide.  Wind  it  on  tightly,  and  at 
intervals  solder  the  whole  width  of  the  band  to- 
gether. 

The  connections  to  the  commutator  should  be 
made  either  by  screws  or  solder,  but  perhaps  best 
by  both.  In  some  cases  it  is  thought  that  it  is 
better  not  to  connect  the  wires  directly  to  the 
commutator  bars,  but  to  solder  them  to  flat  strips, 
which  may  be  bent  around  the  wires  to  make  a 
better  connection,  and  then  screw  and  solder  these 
strips  to  the  commutator  bars,  their  shape  allow- 
ing them  to  make  a  better  contact  than  the  round 
wires. 

Understand  each  loop,  that  is  to  say,  the  begin- 
ning of  one  coil  and  the  ending  of  the  adjacent  one 
is  to  be  connected  to  a  bar  by  itself.  When  the 
connections  are  all  made,  and  the  armature  is  in 
shape  for  running,  it  must  be  balanced.  This  is 
done  by  placing  the  two  ends  of  the  shaft  upon  a 
couple  of  straight  edges,  which  have  previously 
been  carefully  levelled. 

The  armature  will  usually  come  to  rest  in  some 
particular  position,  which  shows  that  the  top  side 
needs  more  weight.  If  it  is  badly  out  of  balance, 
some  pieces  of  lead  should  be  wedged  under  the 
binding  band,  but  if  only  a  little  off,  add  a  little 
solder  to  the  binding  wire  on  the  light  side,  until 
the  armature  will  stay  in  any  position  you  put  it. 


ARMATURE   AND   FIELD-MAGNET   WINDING.  29 

Before  leaving  the  Gramme  ring  armature  we  will 
speak  of  armatures  for  four  pole  machines,  which 
are  or  may  be  slightly  different  from  the  ordinary 
two  pole  armature.  (See  Figs.  16  and  17.)  The 
connection  between  the  winding  and  the  com- 
mutator may  be  the  same  as  for  the  two  pole 
machine,  in  which  case  four  brushes  will  be 
necessary  as  in  the  first  sketch.  The  brushes 
nearest  each  other  will  have  the  opposite  sign 
(-[-  or  — )  and  consequently  those  diametric- 
ally opposite  will  have  the  same  sign.  Two  op- 
posite brushes,  then,  must  be  connected  together 
for  one  pole  of  the  machine,  and  the  other  two  for 
the  other  pole.  It  is  not  necessary  to  use  four 
brushes,  however,  if  the  connections  are  made  as 
shown  in  Figure  17.  Here  the  opposite  seg- 
ments of  the  commutator  or  the  wires  leading 
to  them  are  connected,  which  amounts  to  the  same 
thing  as  connecting  the  opposite  brushes. 

Another  point  should  be  spoken  of  here,  although 
it  applies  equally  to  the  drum  armature,  and  that  is 
the  open  coil  connections.  In  this  armature  there 
are  twice  as  many  commutator  segments  as  coils, 
and  the  ends  of  each  coil  instead  of  being  con- 
nected to  neighboring  segments,  are  connected  to 
the  diametrically  opposite  segments  and  only  one 
end  to  each  segment.  There  is  then  no  connection 
between  the  different  segments. 

A  rather  novel  form  of  Gramme  ring  machine, 


30  AliMATUKE    AND   FIELD-MAGNET  WINDING. 


FIG.  1 6. 


ATCMATUltE    AND    FIELD-MAGNET  WINDING.  81 

which  is  perhaps  better  adapted  for  use  as  a 
motor  than  a  dynamo  will  be  described  while  we 
are  still  on  the  subject  of  ring  armatures.  The 
armature  is  of  the  ordinary  ring  pattern,  preferably 
with  projecting  lugs  on  the  inside  between  the  coils. 


FIG.  18. 

The  field  instead  of  being  around  the  armature  is 
inside  it,  and  is  simply  a  shuttle-wound  armature 
supplied  with  a  current  in  one  direction  only. 
This  gives  a  very  short  magnetic  circuit  and  con- 
sequently requires  but  little  magnetizing  power. 
(See  Fig.  18.) 


32  ARMATUKE    AND    FIELD-MAGNET   WINDING. 


CHAPTER  III. 

DRUM      WINDING. 

THE  drum  armature  is  as  stated  in  the  previous 
chapter,  better  adapted  for  low  potentials  than 
the  ring  armature.  It  has  a  greater  capacity  for 
large  currents  than  the  lines  of  magnetic  force, 
which  means  a  stronger  field. 

Formerly  the  practice  was  to  place  a  number 
of  layers  of  wire  on  the  armature  to  obtain  the 
necessary  E.  M.  F.,  but  while  this  custom  exists 
still  in  the  ring  armatures,  the  tendency  in  the  case 
of  drum  armatures  has  been  to  reduce  the  number 
of  layers  as  much  as  possible,  and  to  make  up  for 
the  loss  of  potential  caused  by  the  fewer  turns  by 
strengthening  the  field  and  increasing  the  speed, 
or  the  diameter  of  the  armature.  The  reason  for 
this  is  that  people  are  beginning  now  to  see 
the  importance  of  reducing  the  resistance  of 
the  magnetic  circuit  to  its  lowest  limit.  The 
gain  affected  by  leaving  off  one  layer  of  wire, 
and  diminishing  the  air  space  between  the  core  and 
pole  pieces  by  that  amount,  is  astonishing  to  one 
who  has  never  seen  it  tried. 


ARMATURE    AND    FIELD-MAGNET  WINDING. 

It  is  even  stated  that  the  pole  pieces  should  fit 
the  armature  winding  so  closely,  that  they  have  to 
be  bored  out  in  shallow  grooves  where  the  bands 
of  binding  wire  come,  and  persons  who  have  tried 
this,  claim  that  the  benefit  resulting  from  it  is 
much  in  excess  of  the  slight  additional  work  it 
makes. 

We  cannot  impress  the  fact  too  forcibly  upon 
our  readers,  then,  that  they  should  make  every 
effort  to  keep  down  this  magnetic  resistance. 
Builders  generally  nowadays  are  trying  to  get  along 
with  a  single  layer  of  wire  on  the  armature.  Wind- 
ing two  layers  has  other  disadvantages.  It  makes 
it  worse  about  getting  at  a  fault  to  repair  it,  and 
does  not  allow  such  good  ventilation.  When  two 
layers  are  wound  on,  it  usually  means  that  one-half 
of  the  armature  winding  is  in  the  first  layer,  and 
the  other  half  in  the  second,  and  that  the  second 
having  a  greater  length  of  wire  has  a  greater  resist- 
ance which  throws  the  armature  out  of  electrical 
balance,  causing  sparking  and  other  evils. 

Various  ingenious  devices  have  been  used  by  in- 
ventors to  overcome  this  last  difficulty,  by  winding 
with  double  wires,  so  that  the  outside  and  inside 
layers  may  have  equal  shares  of  each  coil,  but  they 
are  at  best  make  shifts  and  greatly  increase  the 
trouble  of  construction,  and  we  should  advise  in  all 
cases  when  the  necessary  potential  cannot  be  se- 
cured, except  by  a  large  number  of  turns,  that  a 
Gramme  armature  be  used. 


34  ARMATUKE   AND    FIELD-MAGNET   WINDING. 

The  drum  winding  is  not  essentially  different 
from  the  ring,  except  of  course  that  the  wires  go 
completely  around  the  length  of  the  armature  in 
place  of  passing  through  its  center.  The  same 
remarks  apply  to  lamination  of  the  core,  and  to  the 
pegs  for  keeping  the  wire  in  place.  The  disks  can 
be  held  in  place  on  the  shaft  by  washers  which  can 
be  screwed  against  them  along  the  shaft  from  either 
end.  (See  Fig.  19.) 


"  FIG.  19. 

In  laying  out  the  spaces  on  the  core  to  be  occu- 
pied by  the  coils,  you  must  have  double  the  num- 
ber of  spaces  that  you  have  coils,  if  you  intend  to 
have  only  a  single  layer  of  wire,  for  each  coil  occu- 
pies two  spaces,  one  at  each  end  of  a  diameter  of 
the  core.  If  you  have  two  layers  of  wire  and  wind 
one-half  of  your  wire  in  the  first,  and  the  other 
half  in  the  second  layer,  you  will  only  need  the 


ARMATURE    AND   FIELD-MAGNET  WINDING.  35 

same  number  of  spaces  as  coils.  This  is  a  point 
that  sometimes  puzzles  young  amateurs.  They 
have  only  the  same  number  of  spaces  as  coils  and 
find  to  their  surprise  when  they  have  filled  all  the 
spaces  that  they  have  only  commutator  connec- 
tions for  half  of  the  commutator  bars. 

When  you  are  winding  on  two  layers  of  wire 
you  start  as  you  did  in  winding  the  Gramme  ring,  by 
leaving  a  loose  end  hanging,  and  then  winding  along 
the  length  of  the  armature  and  into  the  spaces 
diametrically  opposite  When  you  have  filled  one 
space  leave  a  loop  hanging,  and  go  on  and  wind  up 
the  next  in  the  same  way.  When  you  have  half 
your  coils  wound,  you  will  find,  as  stated  above, 
that  all  the  spaces  are  occupied.  Shellac  the  wind- 
ing well  and  cover  it  over  with  a  strip  of  cloth. 
The  wires  of  the  different  coils  will  cross  at  the 
ends  of  the  armature.  These  points  of  intersec- 
tion must  always  be  covered  by  a  piece  of  cloth  be- 
fore the  next  coil  goes  on. 

Wind  the  second  half  of  the  armature  over  the 
top  of  the  first  one  and  connect  the  last  end  with 
the  starting  wire  of  the  first  layer.  When  wind- 
ing, as  in  this  case,  into  diametrically  opposite 
spaces,  you  will  find  that  the  armature  shaft  inter- 
feres with  the  wire  going  straight  across  the  end 
and  you  will  have  to  go  around  it,  one-half  the  coil 
on  one  side  and  one-half  on  the  other.  The 
armature  shaft  at  this  point  must  be  insulated  as 


ARMATURE    AND   FIELD-MAGNET   WINDING. 

thoroughly  as  the  core  itself.  When  winding  on 
only  one  layer,  we  proceed  in  a  slightly  different 
manner. 

Suppose,  for  example,  that  we  have  a  four-coil 
armature.  Then  beginning  at  one  of  the  spaces, 
wind,  not  into  the  diametrically  opposite  one  but 
into  its  neighbor. 


H 


FIG.  20. 


Beginning  at  a,  wind  the  coil  1-2,  and  throw 
out  a  loop,  and  skipping  space  b,  wind  coil 
3-4.  Throw  out  a  loop  again  and  skipping  d,  wind 
5—6,  and  lastly  skipping  fy  wind  7-8,  and  join  the 
two  ends,  and  connect  to  the  commutator  as 
shown.  This  method  is  to  be  followed  for  any 
number  of  coils.  We  simply  wind  into  an  adja- 
cent space  to  the  one  diametrically  opposite  the 


ARMATUKE    AND    FIELD-MAGNET   WINDING.  37 

starting  space,  and  then  skip  a  space  in  starting 
the  next  one.      (See  Fig.  20.) 

The  remarks  about  finishing  up  the  ring  arma- 
ture all  apply  equally  to  the  drum  armature. 

We  will  now  take  up  the  theoretical  armature 
and  the  methods  of  making  our  calculations.  The 
formula  given  above,  for  the  E.  M.  F.  of  the  arma- 
ture is 

E=l  t  N  ^ 

This  expression  if  the  lines  of  force  /  are  given 
in  absolute  units  would  give  the  E.  M.  F.  in  abso- 
lute units.  The  absolute  unit  is  TOOO^OO^TT  of  the 
practical  unit  or  volt,  so  we  must  divide  the  result 
above  by  100000000  to  get  it  into  volts  or  what 
means  the  same  thing,  multiply  it  by  io"8. 

If  we  adopt  the  Kapp  notation  and  make  our 
unit  of  field  strength  6,000  times  as  large  as  the 
absolute  unit,  and  call  the  strength  of  field  as 
expressed  by  this  new  unit  Z,  we  should  have  for 
the  relation  between  Z  and  / 
l=6ooo  Z. 

Z  and  /  are  the  number  of  lines  of  force,, 
which,  for  a  given  field  will  vary  inversely  as  the 
size  of  the  unit.  If  we  use  this  new  unit  we  must 
divide  the  result  by  1,000,000  instead  of  100,000,000 
to  get  E  in  volts  and  will  have 

ZtNn    -7  f  M  n    irT8 

— Toooooo —  ^  t  IN  n  IO 

If  we  let  m  equal  the  number  of  lines  of  force  per 
square  inch  of  section  of  armature  core  and  a  be 


38  ARMATURE    AND   FIELD-MAGNET   WINDING. 

the  length  of  the  core  and  b  equal  its  thickness 
then  2  abm  will  equal  the  number  of  lines  of 
force  passing  through  the  core  in  the  case  of  the 
Gramme  ring  and  abm  in  the  case  of  the  drum 
armature.  (See  Fig.  21.) 


FIG.  21. 

M  according  to  Kapp  reaches  its  maximum  when 
it  equals  30,  and  the  iron  is  then  said  to  be  satu- 
rated ;  20,  according  to  the  same  authority  is  a 
fair  average  value  for  good  modern  dynamos  and 
motors. 


ARMATUHE    AND    FIEI.D-MAGXET   WINDING.  39 


CHAPTER   IV. 


FIELD      WINDING. 

THE  magnetic  field  in  which  the  armature  re- 
volves may  be  produced  by  permanent  or  electro- 
magnets. The  first  method  makes  a  bulky  machine 
for  the  hardened  steel,  of  which  such  magnets  are 
made  is  an  inferior  conductor  of  magnetic  force 
to  wrought  or  cast  iron.  It  has  given  away  in  ma- 
chines meant  to  supply  any  considerable  current, 
to  the  electro-magnetic  field,  but  is  still  used  on  the 
"magnetos"  for  ringing  bells  and  for  therapeutical 
purposes.  In  such  cases  it  is  customary  to  use  a 
shuttle  armature  with  fine  wire  winding  and  no 
commutator. 

It  is  stated  that  permanent  magnets  are  much 
better  adapted  for  dynamos  than  motors,  as  in  the 
former  case  they  tend  to  become  stronger  and  in 
the  latter  weaker  through  use.  In  every  case  how- 
ever where  the  machine  is  of  any  size,  and  space  and 
weight  an  object,  the  iron  fields  are  vastly  superior 
since  a  given  weight  of  iron  will  give  a  much 
stronger  field  than  an  equal  weight  of  hardened 
steel,  of  the  same  shape. 


40  ARMATURE    AND   FIELD-MAGNET   WINDING. 

The  magnetic  qualities  of  the  iron  are  conferred 
upon  it  by  a  winding  of  insulated  wire  through 
which  a  current  is  passing.  Theoretically  there 
should  be  no  difference  in  the  magnetic  force  pro- 
duced by  a  given  coil  of  wire  and  current,  no  mat- 
ter at  what  point  of  the  magnet's  length  it  is  placed. 
And  really  there  is  not,  but  there  seems  to  be  a 
general  idea  among  dynamo  constructors,  that 
coils  put  upon  the  poles  or  close  to  them,  prevent 
the  lines  of  force  from  straying  around  in  some 
other  way  than  through  the  armature  where  they 
will  do  some  useful  work.  It  is  mainly  -for  this 
reason  that  we  see  the  series  coils  of  so  many 
dynamos  placed  upon  the  poles.  There  are  also 
the  advantages  of  greater  accessibility  for  repairs, 
and  less  damage  from  over  heating. 

In  winding  a  magnet  it  makes  no  difference  so 
far  as  the  magnetic  effect  is  concerned,  whether 
there  are  100  turns  of  wire  with  I  ampere  flowing 
through  them,  or  I  turn  with  100  amperes.  The 
product  of  the  number  of  turns  by  the  amperes  is 
called  the  "ampere-turns." 

The  fields  of  different  dynamos  may  be  wound 
very  differently  but  have  the  same  strength.  The 
fields  of  a  shunt  wound  dynamo  get  their  current 
at  a  constant  potential,  and  as  it  is  desirable  to  use 
as  little  power  as  possible  on  them,  the  winding  is 
made  of  fine  wire  to  give  a  high  resistance,  and 
the  small  amount  of  current  is  made  up  for  by 
the  larger  number  of  turns. 


ARMATURE   AND   FIELD-MAGNET  WINDING.  41 

In  a  series  wound  dynamo  there  is  usually  a  cer- 
tain amount  of  current  available,  and  it  is  taken 
around  the  fields  on  large  wire,  and  with  as  few 
turns  as  possible.  The  character  of  the  winding 
will  depend  therefore  upon  the  conditions  under 
which  the  dynamo  is  to  run. 


42  ARMATURE    AND    FIELD-MAGNET   WINDING. 


CHAPTER  V. 


FIELD      FO  RMUL AE . 

THE  calculations  for  the  strength  of  the  field, 
and  the  necessary  current  to  produce  it,  are  based 
upon  the  assumption  that  the  lines  of  magnetic 
force  obey  a  similar  law  to  that  for  electric  current, 
viz. ;  that  they  vary  directly  as  the  magnetizing  force 
and  inversely  as  the  resistance  of  the  circuit. 
Kapp  has  made  this  a  subject  of  investigation  and 
finds  a  formula  which  fits  approximately  to 
observed  facts.  This  is  given  below  : 

P_ 

Z— 1 440*1+  i  +^ 

h     cb     '     ab     '     AB 

and 
0.8  P 


_-. 

'     ab     '     AB 

Where  Z=  the  total  number  of  lines  of  force, 
P  the  exciting  power  in  ampere-turns,  a  b  the  cross 
section  of  the  armature  (Gramme  ring  in  this  case), 
c  the  arc  spanned  by  each  pole  piece,  d  the  distance 
between  the  polar  surface  of  the  magnets  and  the 
external  surface  of  the  armature  core,  1  the  average 


ARMATURE   AND    FIELD-MAGNET  WINDING. 


43 


length  of  the  magnetic  circuit  inside  the  armature, 
L  the  length  of  the  magnetic  circuit  in  the  field 
magnets,  and  A  B  the  cross  sectional  area  of  their 
core.  See  Fig.  22. 

As  the  lengths  are  all  given  in  inches,  the  excit- 
ing power  in  ampere-turns,  and  the  result  Z  in  the 
same  units  chosen  in  the  armature  formula  viz. :  6000 
times  larger  than  the  absolute  unit,  so  that  the 


FIG.  22. 

results  obtained  by   this  formula  may  be  readily 
applied  to  the  armature  calculations. 

The  first  of  the  two  formulae  is  for  well  an- 
nealed wrought  iron,  and  a  wrought  iron  armature 
core,  the  second  is  for  cast  iron  magnets.  The 
formulae  only  apply  where  the  degree  of  magne- 


44 


ARMATURE   AND   FIELD-MAGNET   WINDING. 


tization  of  the  field  core  is  not  higher  than  10  lines 
per  square  inch,  and  there  give  pretty  fair  results. 
Higher  degrees  of  magnetization  demand  more 
current  than  the  formulae  call  for,  and  when  the 
saturation  point  is  approached,  the  increased  power 
necessary  over  that  given  in  the  formulae  is  from 
40  to  100  ft. 

Different  specimens  of  iron  will  sometimes  vary 
in  their  magnetic  qualities,  to  such  an  extent  that 


FIG.  23. 

a  formula  will  often  not  serve  a  much  better  pur- 
pose than  a  foundation  upon  which  to  base  a  good 
guess.  The  formulae  of  Kapp  however  are  about 
the  best  that  have  been  brought  out  as  yet,  and  are 
near  enough  to  the  truth  to  enable  one  to  build  a 
dynamo,  and  not  come  very  far  from  the  calculated 
output.  By  multiplying  the  Z  by  the  denomi- 
nator of  the  fraction  in  the  second  term  we  get 
the  value  of  P  or  the  ampere-turns  which  we 


ARMATURE   AND   FIELD-MAGNET  WINDING.  45 

must  use  upon  our  magnets.     The  formulae  where 
double  magnetos  are  used,  are 


for  wrought  iron  and  for  cast  iron 
Z_  0.8  P 

2 


The  double  field  magnet  can  be  made  lighter 
than  the  single  one  for  the  same  power,  but  re- 
quires more  copper.  Where  expense  is  an  item 
to  be  considered  it  must  give  way  to  the  single 
magnet,  but  where  weight  is  the  chief  point,  it  is 
to  be  preferred.  (See  Fig.  23.) 


46  ARMATUBE   AND   FIELD-MAGNET   WINDING. 


CHAPTER   VI. 


GENERAL  METHODS  OF*   WINDING. 

AN  experimental  method  of  determining  the 
winding  will  next  be  considered.  This  is  not  only 
useful  in  itself  but  can  be  applied  advantageously 
as  a  check  upon  the  calculations  described  in  the 
previous  chapter. 

The  armature  is  supposed  to  be  wound,  and  the 
field  cores  ready  to  receive  their  wire.  Put  the 
armature  in  place  and  start  it  to  revolving  at  the 
speed  you  desire  it  to  have.  Put  a  few  turns  of 
large  wire  around  the  field  cores  and  pass  a  current 
over  them  from  some  independent  source.  Take 
the  current  off  your  armature  through  some  adjust- 
able resistance— a  bank  of  incandescent  lamps  makes 
a  good  one  where  it  can  be  had  and  a  water  resistance 
is  also  good.  This  is  made  by  putting  two  metallic 
electrodes  in  a  vessel  of  water  and  arranging  them 
so  that  the  distance  between  them  can  be  altered. 
A  resistance  varying  from  a  high  to  a  low  limit 
can  be  had  by  using  pure  water,  and  adding  a  drop 
or  two  of  sulphuric  acid  per  gallon.  Pure  water 
will  give  a  high  resistance  and  the  acid  lowers  it. 


AKMATUKE   AND    FIELD-MAGNET   WINDING.  47 

The  finer  adjustment  is  made,  after  you  have 
about  what  you  want  in  this  way,  by  altering 
the  distance  apart  of  the  electrodes.  Iron  tel- 
egraph wire  also  makes  a  good  resistance,  coiled 
up  in  springs,  or  wound  around  a  wooden  frame. 
Vary  this  resistance  and  the  current  around  your 
fields  until  you  get  the  required  current  and  E.  M. 
F.  from  your  armature.  Then  note  the  current  in 
the  wire  around  your  fields,  and  the  number  of 
turns  and  you  have  the  ampere  turns  necessary  to 
give  the  required  strength  of  field. 

As  explained  above,  it  makes  no  difference  how 
these  ampere  turns  are  put  on,  so  that  only  a  few 
turns  of  wire  are  necessary  for  the  experiment, 
providing  you  have  sufficient  current. 

Then  comes  the  question  as  to  what  size  wire  to 
use  on  the  fields.  In  a  series  wound  machine  this 
is  simply  a  question  as  to  what  size  wire  will  carry 
the  current  without  overheating,  for  your  amperes 
are  already  decided  by  the  current  that  comes  from 
the  armature,  and  you  have  simply  to  divide  the 
ampere  turns  as  determined  above  by  this,  to  get 
the  number  of  turns. 

In  the  case  of  a  shunt  wound  machine  it  is  dif- 
ferent. Here  you  have  a  certain  E.  M.  F.  avail- 
able and  you  must  adjust  your  field  winding  so 
that  it  will  produce  the  requisite  number  ampere 
turns. 

Here   comes   in  a  little  point  upon  which  good 


48  ARMATURE    AND    FIELD-MAGNET   WINDING. 

men  trip  up,  and  which  the  author  has  never  seen 
mentioned  in  text  books.  It  does  not  make 
any  difference,  once  the  size  of  wire  on  the 
fields  is  chosen,  how  many  turns  you  put  on  if 
your  dynamo  or  motor  is  shunt  wound.  For  ex- 
ample, suppose  you  have  ten  turns  of  wire  of  such 
a  size  that  with  the  given  E.  M.  F.  of  the  machine 
it  will  allow  fifteen  amperes  to  flow  over  it.  This 
will,  of  course,  mean  150  ampere  turns  on  the 
magnet.  Suppose,  with  the  E.  M.  F.  unchanged, 
you  increase  the  number  of  turns  to  20.  This  will 
double  the  resistance  of  the  wire  and  consequently 
cut  down  the  current  to  half  its  original  strength, 
or  to  seven  and  a  half  amperes.  Multiplying  this 
by  20  we  again  get  150  for  the  ampere  turns,  and 
this  would  hold  true  in  whatever  way  we  change 
the  number  of  turns,  keeping  the  E.  M.  F.  and 
size  of  wire  constant.  This  will  not  be  strictly 
accurate  where  we  have  several  layers  of  wire, 
since  the  outer  layers  will  be  longer  than  the 
inner  ones  and,  consequently,  have  a  greater  re- 
sistance. If  the  diameter  of  the  core  bears  a  large 
ratio  to  the  thickness  of  the  layer  of  wire  upon  it 
the  rule  will  be  nearly  enough  right  for  all  practi- 
cal purposes. 

Suppose,  then,  that  we  have  found  out  the  num- 
ber of  ampere  turns  and  know  what  E.  M.  F.  we 
are  to  have.  Dividing  the  E.  M.  F.  in  volts  by  the 
number  of  ampere  turns  we  get  the  resistance 


ARMATURE    AND   FIELD-MAGNET   WINDING.  49 

required  of  a  single  turn  of  wire  around  the  fields 
to  give  the  required  number  of  ampere  turns. 
Find  the  average  length  of  one  turn  of  wire  and 
from  a  wire  table  find  the  size  of  wire  which  has 
the  desired  resistance  for  this  length.  This  is  the 
size  wire  to  use.  Of  course,  a  single  turn  of  this 
wire  would,  under  ordinary  circumstances,  be 
burnt  up  by  putting  it  on  the  E.  M.  F.  of  the 
machine,  so  we  must  put  on  a  large  number  of 
turns,  reducing  the  current  in  consequence,  until 
we  have  it  too  small  to  do  any  damage.  It  will 
easily  be  seen  that  the  greater  number  of 
turns  we  put  on  the  less  energy  necessary  to 
magnetize  the  fields,  for  more  turns  means  a 
higher  resistance  or  less  current,  and  the  energy 
used  on  the  fields  being  equal  to  the  current 
through  them,  multiplied  by  the  E.  M.  F.,  it  natur- 
ally follows  that  it  is  reduced  in  the  same  propor- 
tion that  the  turns  are  increased. 

It  might  seem  at  first  as  if  we  might,  by  increas- 
ing the  amount  of  copper  on  the  fields,  come  at 
last  to  the  point  where  no  energy  is  required  to 
rim  them,  but  of  course  this  would  be  impractica- 
ble, for  it  would  mean,  in  the  first  place,  a  resist- 
ance equal  to  infinity,  and  in  the  second,  that  the 
layer  would  have  to  be  so  thick  that  the  rule  given 
above  would  no  longer  hold  true.  There  is  a  limit 
depending  upon  the  money  interest  or  the 
copper  used,  and  the  cost  of  the  energy  lost.  A 


50  AKMATURE    AND   FIELD-MAGNET   WINDING. 

process  similar  to  that  used  by  Sir  William  Thom- 
son in  determining  the  proper  amount  of  copper 
to  use  on  a  certain  piece  of  wiring  could  be  applied 
here,  but  this  is  an  unnecessary  piece  of  refinement 
and  all  that  is  really  needful  is  to  see  that  the  wire 
is  long  enough  to  reduce  the  current  within  safe 
limits. 

Often  it  will  be  found  that  no  size  of  wire  given 
in  the  table  will  give  the  exact  resistance  called  for, 
and  in  that  case  you  will  have  to  use  two  different 
sizes  which  fall  on  each  side  of  the  required  resist- 
ance, winding  a  few  layers  with  one,  and  the  rest 
with  the  other.  This  is  also  the  course  to  pursue, 
if  the  winding  when  completed  fails  to  give  the 
desired  result.  Unwrap  a  layer  or  two  and  rewind 
with  a  different  size  wire,  larger  or  smaller  accord- 
ing as  you  wish,  the  fields  to  be  stronger  or  weaker. 

The  experimental  method  answers  very  nicely  for 
getting  the  data  for  compounding  a  machine. 
Run  your  dynamo  first  unloaded  and  measure  the 
ampere  turns  as  directed  above,  necessary  to  give 
the  E.  M.  F.  Then  run  it  on  the  full  load  and 
again  get  the  ampere  turns.  The  first  will  give 
you  the  ampere  turns  for  the  shunt  winding,  and 
the  difference  between  the  first  and  second,  the 
ampere  turns  for  the  series.  As  this  is  not  always 
an  even  number  it  is  customary  in  some  places  to 
make  the  series  coil  larger  than  is  really  necessary, 
and  then  put  a  German  Silver  shunt  across  its  ends 


ARMATURE    AND   FIELD-MAGNET   WINDING.  51 

which  will  reduce  the  current  in  it  to  the  proper 
amount.  This  series  coil  is  generally  placed  as 
near  the  pole  pieces  as  possible,  and  is  often  made 
of  flat  strips  of  copper,  these  requiring  less  room 
than  round  wire  and  being  better  adapted  to  radiate 
the  heat. 

In  making  the  above  calculations  some  allowance 
must  be  made  for  the  increased  resistance  caused 
by  the  rise  in  temperature.  In  the  series  machine 
this  does  not  play  any  part,  as  the  current  has  to 
get  over  the  coils,  but  in  the  case  of  the  shunt 
coils  where  the  current  is  determined  by  the  re- 
sistance, this  must  be  taken  into  account.  The 
rise  in  resistance  due  to  temperature  is  .21^0  for 
every  degree  Fahrenheit.  And  it  is  well  not  to  let 
the  wire  get  much  above  110°  or  1200,  and  a 
lower  temperature  means  much  less  waste  of 
energy. 

The  old  rule  for  the  safe  carrying  capacity  of 
copper  wire,  is  to  allow  one  square  inch  cross  sec- 
tion of  wire  for  1,000  amperes  of  current  where 
the  wire  is  by  itself,  and  one  square  inch  cross  sec- 
tion for  400  or  500  amperes  in  places  where  the 
wire  is  covered  or  surrounded  by  other  wires. 
Prof.  Forbes  says  that  wires  used  in  winding  which 
are  2  millimetres  in  diameter  will  carry  5  to  6  am- 
peres per  square  millimetre,  and  that  wire  5  mil- 
limetres in  diameter  will  carry  3  amperes  per  square 
millimetre. 


52  ARMATURE    AND    FIELD-MAGNET   WINDING. 


CHAPTER   VII. 

FIELD     WINDING. 

The  method  of  winding  will  depend  largely 
upon  the  form  of  the  field  core,  and  we  will  briefly 
discuss  that  before  going  further. 

Cast  iron  cores  will,  in  most  cases,  be  cheapest 
to  construct,  but  a  wrought  iron  core  is  always  the 
most  effective  electrically,  as  the  formulae  given 
above  show.  A  cast  iron  core  can  be  made  almost 
any  shape,  but  there  is  a  limit  to  the  number  of 
shapes  in  which  wrought  iron  can  be  made,  unless 
an  expensive  amount  of  forging  is  done. 

One  wrought  iron  form,  which  can  be  made 
without  much  trouble,  is  given  in  Fig.  24. 

After  bending  into  shape,  the  space  for  the 
armature  can  be  bored  out  and  the  winding  slipped 
over  spools. 

Another  of  the  same  style  is  shown  in  Fig.  25. 

In  this  case  it  would  be  well  to  make  it  in  two 
pieces,  and  bolt  together  at  A  and  B.  This  makes 
it  easier  to  get  the  winding  on. 

Often  the  cores,  and  perhaps  yoke  of  the  fields, 
are  made  of  wrought  iron,  as  they  are  ordinarily 


ARMATURE   AND   FIELD-MAGNET   WINDING. 


53 


square  or  round  pieces,  and  the  poles  made  of 
cast  iron.  The  poles  should,  in  this  case,  be  made 
more  massive  in  proportion  to  the  other  parts  than 
if  they  were  wrought  iron. 

In  general,  it  is  not  advisable  to  have  too  many 
breaks  across  the  paths  of  the  lines  of  force,  and 


FIG.  24. 


FIG.  25. 

for  this  reason  the  author  does  not  think  that  one 
form  of  field  he  has  seen  described  is  very  desira- 
ble, except  for  small  machines,  although  it  is  of 
the  best  wrought  iron.  It  is  made  of  a  strip  of 
sheet  iron,  wrapped  around  a  former,  until  the  right 
thickness  is  obtained.  The  lines  of  force  have  a 
free  path  until  they  come  to  get  into  the  armature, 


54  ARMATL'BE   AND   FIELD-MAGNET   WINDING. 


FORMS    OF   FIELD    MAGNETS 


AKMATUUE    AND    FIELD-MAGNET    WINDING.  55 


[/-~\l 


FORMS   OF    FIELD    MAGNETS. 


56 


ARMATURE    AND    FIELD-MAGNET   WINDING. 


and  then  they  have  to  jump  across  from  face  to 
face  of  the  sheets.     (See  Fig.  26.) 

A  better  way,  and  one  adopted  by  a  certain 
prominent  company,  is  to  stamp  out  sheets  of  iron 
into  the  proper  shape  and  then  bind  them  together 
with  the  plane  of  their  faces  running  lengthwise 
of  the  magnet,  but  at  right  angles  to  the  way 
shown  above.  The  pole  pieces  should  not  embrace 


FIG.  26. 

the  armature  more  than  the  diameter  of  the  arma- 
ture core.     (See  Fig  27.) 

Nor  should  they  project  beyond  the  ends  of  the 
core  for  the  reasons  given  in  speaking  of  the 
armature.  The  wire  should  always,  where  it  is 
possible  to  do  so,  be  wound  in  a  lathe,  as  it  is  much 
less  tedious  and  can  be  done  more  evenly.  It  can 
be  wound  directly  upon  the  field  core,  or  may  be 
wound  upon  a  spool  and  slipped  over  the  core 
afterwards.  (See  Fig.  28.) 


ABMATUIiE    AND    FIELD-MAGNET   WINDING. 


57 


This  spool  is  generally  made  of  sheet  iron  to  fit 
closely  upon  the  core,  and  is  flanged  at  the  open 
ends  to  the  depth  of  the  winding.  A  flange  made 
of  brass,  with  the  edges  polished,  gives  a  very 
neat  appearance.  A  spool  is  generally  used  where 
it  is  impossible  to  swing  the  cores  in  a  lathe. 

A  double  magnet,  made  in  a  solid  piece,  will 
have  to  be  wound  by  hand,  as  it  is  impossible  to 
swing  it  in  a  lathe  or  to  put  on  a  spool.  Such 


FIG.  27. 

forms  in  general  should  be  avoided.  Before 
commencing  to  wind,  the  bare  metal  must  be  in- 
sulated with  a  couple  of  thicknesses  of  yellow 
wrapping  paper  laid  on  with  shellac.  The  starting 
end  of  your  wire,  if  the  wire  be  small,  must  be 
soldered  to  a  larger  piece  of  wire,  preferably 
with  waterproof  insulation,  and  this  piece  lead 
out  through  a  hole  in  one  of  the  flanges  to 
make  the  connection.  Wind  the  wire  on  in  even 


58  ABMATUBE    AND   FIELD-MAGNET    WINDING. 

layers  and  drive  the  coils,  every  dozen  turns,  back 
upon  themselves  with  a  smooth  piece  of  wood  and. 
a  light  hammer,  being  careful  not  to  abrade  the 
insulation.  Double  cotton-covered  copper  wire 
should  be  used  both  for  armature  and  fields.  Shel- 
lac each  layer  as  you  finish  it  and  cover  it  with  a 
piece  of  paper  before  beginning  the  next.  The 
wire  must  be  drawn  tight  enough  to  insure  the 
wire  lying  snugly.  This  tension  is  produced  by 
taking  the  wire  around  a  number  of  grooved 


FIG.  28. 

wooden  wheels  which  turn  rather  stiffly,  but  not 
enough  so  that  the  wire  will  slide  over  them.  (See 
Fig.  29.) 

When  you  commence  to  wind  the  next  to  the 
last  layer,  tie  a  piece  of  string  around  the  first  turn 
of  wire  and  leave  the  ends  hanging  loose,  and  when 
you  return  to  that  end,  winding  the  last  layer,  tie 
the  last  turn  down  by  these  strings,  and  this  will 
prevent  the  wire  coming  loose  when  the  tension  is 
taken  off.  The  winding  should  now  be  baked, 
like  the  armature,  and  is  then  ready  to  be  as- 


AK MATURE   AND   FIELD-MAGNET  WINDING. 


60  ARMATURE   AND   FIELD-MAGNET  WINDING. 

sembled.  The  connections  should  all  be  soldered 
and  taped  over,  and  the  wire  should  be  taped  wher- 
ever it  comes  in  contact  with  the  metallic  work 
about  the  machine. 

Both  fields  and  armature  should  be  tested  to  see 
that  there  is  no  contact  with  the  core  by  trying  to 
ring  a  magneto  from  the  wire  to  the  core,  and  if 
any  contact  is  discovered  it  should  be  fixed  at  once. 
Some  manufacturers  wind  heavy  twine  around 
the  fields  over  the  wire  after  it  is  all  on.  This 


FIG.  30. 

gives  a  neat  appearance  and  protects  the  fine 
wire  from  injury.  The  fields  must  be  con- 
nected up  in  such  a  way  as  to  make  the  pole 
pieces  north  and  south  magnetic  poles.  To 
know  if  the  pole  is  north  or  south,  look  at  the 
winding  at  the  end  from  which  it  projects,  and  if 
the  current  goes  in  the  direction  of  the  hands  of  a 
watch,  the  pole  is  south,  and  if  in  the  contrary 
direction,  north.  (See  Fig.  30.) 

If  more  than  two  poles  are  used,  they  must 
alternate  north  and  south. 

In  making  the  armature  and  field  connections, 


ARMATURE   AND   FIELD-MAGNET  WINDING.  61 

you  must  be  careful  to  get  the  machine  connected 
for  the  way  in  which  it  is  to  run.  A  dynamo  or 
motor  will  not  run  in  either  direction  indifferently. 

If  you  run  the  dynamo  in  the  wrong  direction, 
you  get  no  current. 

First  make  up  your  mind  which  way  the  machine 
is  to  run,  and  then  follow  up  the  current  and  see 
if  it  will  magnetize  the  fields  in  the  proper  direc- 
tion. If  it  will  not,  your  connection  must  be 
reversed. 


ARMATURE   AND   FIELD-MAGNET   WINDING. 


Table  of  Dimensions  and  Resistances  of  Pure 
Copper  Wire.* 

REVISED. 


No. 
B.  &S. 

Diam. 
Mils. 

Area. 

W'gt  &  Length.  Sp.  gr.  8.9 

Circular 
Mils. 

Square 
Inches. 

Lbs. 
per 
1000  ft. 

Pounds 
per 
mile. 

Feet 
per 
pound. 

0000 
000 
00 
0 

460.000 
409.640 
364.800 
324.950 

211600.0 
167805.0 
133079.0 
105592.5 

166190.2 
131793.7 
104520.0 
82932.2 

640.73 
508.12 
402.97 
319.74 

3383  04 
2682.85 
2127.66 
1688.20 

I.o6 
1.97 
2.48 
3.13 

1 

2 
3 
4 
5 

289.300 
257.630 
229.420 
204.310 
181.940 

83694.5 
66373.2 
52633.5 
41742.6 
33102.2 

65733.5 
52129.4 
41338.3 
32784.5 
25998.4 

253.43 
200.98 
159.38 
126.40 
100.23 

1338.10 
1061.17 
841.50 
667.38 
529.23 

3.95 
4.98 
6.28 
7.91 
9.98 

6 
7 
8 
9 
10 

162.020 
144.280 
128.490 
114  430 
101.890 

26250.5 
20816.7 
16509.7 
13094.2 
10381.6 

20617.1 
16349.4 
12966.7 
10284.2 
8153.67 

79.49 
63.03 
49.99 
39.65 
31.44 

419.69 
332.82 
263.96 
209.35 
165.98 

12.58 
15.86 
20.00 
25.22 
31.81 

11 

12 
13 
14 
15 

90.742 
80.808 
71.961 
64.084 
57.068 

8234.11 
6529.94 
5178  39 
4106.76 
3256.76 

6467.06 
5128.60 
4067.09 
3225.44 

2557.85 

24.93 
19.77 
15.68 
12.44 
9.86 

131.65 
104.40 

82.792 
65.658 
52.069 

40.11 

50.58 
63.78 
80.42 
101.40 

16 
17 

18 
19 
20 

50.820 
45.257 
40.303 
35.890 
31.961 

2582.67 
2048.20 
1624.33 
1288.09 
1021.44 

2028.43             7.82 
1608.65             6.20 
1275.75             4.92 
1011.66             3  90 
802.24             3.09 

41.292 
32.746 
25.970 
20.594 
16.331 

127.87 
161.24 
203.31 
256.39 
323.32 

21 
22 
23 
24 
25 

28.462 
25.347 
22.571 
20.100 
17.900 

810.09 
642.47 
509.45 
404.01 
320.41 

636.24 
504.60 
400.12 
317.31 
251.65 

2.45 
1.95 
1.54 
1.22 
.97 

12.952 
10.272 
8.1450 
6.4593 
5.1227 

407.67 
514.03 
648.25 
817.43 
1030.71 

26 
27 
28 
29 
30 

15.940 
14.195 
12.641 
11.257 
10.025 

254.08 
201.50 
159.80 
126.72 
100.50 

199.56 
158.26 
125.50 
99.526 
78.933 

.77 
.61 
.48 
.38 
.30 

4.0623 
3.2215 
2.5548 
2.0260 
1.6068 

1299.77 
1638.97 
2066.71 
2606.13 
3286.04 

31 
32 
33 
34 
35 

8.928 
7.950 
7.080 
6.304 
5.614 

79.71 
63.20 
50.13 
39.74 
31.52 

62.603 
49.639 
39.369 
31.212 
24.753 

.24 
.19 
.15 
.12 
.10 

1.2744 
1.0105 
.8014 
.6354 
.5039 

4143.18 
5225.26 
6588.33 
8310.17 
10478.46 

36 
37 
38 
39 
40 

5.000 
4.453 
3.965 
3.531 
3.144 

25.00 
19.83 
15.72 
12.47 

9.88 

1JK635 
15.574 
12.347 
9.7923 
7.7635 

.08 
.06 
.05 
.04 
.03 

.3997 
.3170 
.2513 
.1993 

.1580 

13209.98 
16654.70 
21006.60 
26427.83 
33410.05 

1  mile  pure  copper  wire  1-16  in.  diam.=13.59  ohms  at  15.5°C  or  59.9°F. 


AKMATUKE    AND    FIELD-MAGNET   WINDING. 


63 


Table  of  Dimensions  and  Resistances  of  Pure 
Copper  Wire.* 

REVISED. 


No. 
B. 

& 
S. 

Resistance  at  75°F. 

Ibs  p.  1000 
ft.  ins'd 
H.B.&H. 
line  wire. 

Feet   per 
Ib.  ins'd 
H.B.&H. 
line  wire. 

R 

ohms  per 
1000  feet. 

Ohms 
per 
mile. 

Feet 
per 

ohm. 

Ohms 
per 
pound. 

4-0 
3-0 
00 
0 

.04904 
.06184 
.07797 
.09827 

.25891 
.32649 
.41168 
.51885 

20392.9 
16172.1 
12825.4 
10176.4 

.00007653 
.00012169 
.00019438 
.00030734 

800 
666 
500 
363 

1.25 
1.50 
2.00 
2.75 

1 
2 
3 
4 

5 

.12398 
.15633 
.19714 
.24858 
.31346 

.65460 
.82543 
1.04090 
1.31248 
1.65507 

8066.0 
6396.7 
5072.5 
4022.9      . 
3190.2 

.00048920 
.00077784 
.0012370 
.0019666 
.0031273 

313 
250 
200 
144 
125 

3.20 
4.00 
5.00 
6.9 
8.0 

6 

7 
8 
9 
10 

IT 

12 
13 
14 
15 

.39528 
.49845 
.62849 
.79242 
.99948 

2.08706 
2.63184 
3.31843 
4.18400 
5.27726 

2529.9 
2006.2 
1591.1 
1262.0 
1000.5 

.0049728 
.0079078 
.0125719 
.0199853 
.0317946 

105 

87 
69 

50 

9.5 
11.5 
14.5 

20.0 

1.2602 
1.5890 
2.0037 
2.5266 
3.1860 

6.65357 
8.39001 
10.5798 
13.3405 
16.8223 

793.56 
629.32 
499.06 
395.79 
313.87 

.0505413 
.0803641 
.127788 
.203180 
.323079 

31 

22 

32.0 
45.0 

16 
17 
18 
19 
20 

4.0176 
5.0660 
6.3880 
8.0555 
10.1584 

21.2130 
26.7485 
33.7285 
42.5329 
53.6362 

248.90 
197.39 
156.54 
124.14 
98.44 

.513737 
.816839 
1.298764 
2.065312 
3.284374 

14 
11 

70.0 

90.0 

21 

22 
23 
24 
25 

12.8088 
16.1504 
20.3674 
25.6830 
32.3833 

67.6302 
85.2743 
107.540 
135.606 
170.984 

78.07 
61.92 
49.10 
38.94 
30.88 

5.221775 
8.301819 
13.20312 
20.99405 
33.37780 

26 
27 
28 
29 
30 

40.8377 
51.4952 
64.9344 
81.8827 
103.245 

215.623 
271.895 
342.854 
432.341 
545.133 

24.49 
19.42 
15.40 
12.21 
9.686 

53.07946 
84.39916 
134.2"05 
213.3973 
339.2673 

31 

32 
33 
34 
35 

130.176 
164.174 
207.000 
261.099 
329.225 

687.327 
866.837 
1092.96 
1378.60 
1738.31 

7.682 
6.091 
4.831 
3.830 
3.037 

539.3404 
857.8498 
1363.786 
2169.776 
3449.770 

36 
37 
38 
39 
40 

415.047 
523.278 
660.011 

832.228 
1049.718 

2191.45 
2762.91 
3484.86 
4394.16 
5542.51 

2.409 
1.911 
1.515 
1.202 
.9526 

5482.766 
8715.030 
13864.51 
22043.92 
35071.11 

•1  mile  pure  copper  wire  1-16  in.  diam.=13.59  ohms  at  15.5°C.  or  59.9°F. 


64  ABMATURE    AND    FIELD-MAGNET   WINDING. 


CHAPTER  VIII. 

DYNAMOS. 

WE  will  now  take  a  brief  survey  of  some  of  the 
dynamo  electric  machines  manufactured  by  the 
leading  companies  of  the  United  States. 

The  Thomson-Houston  Arc  Dynamo. — In  this 
machine  the  field  magnets  are  cup  shaped,  they 
consist  of  two  cast  iron  tubes,  furnished  at  their 
inner  ends  with  hollow  cups,  cast  in  one  with  the 
tubes,  and  accurately  turned  to  receive  the  arma- 
ture ;  upon  these  tubes  are  wound  the  coils  ;  after- 
wards the  magnets  are  united  by  means  of  a  num- 
ber of  wrought  iron  bars,  which  constitute  the 
yoke  of  the  magnet,  and  at  the  same  time  protect 
the  coils.  The  magnets  are  carried  on  a  frame- 
work, which  also  supports  the  bearings  for  the 
armature  shaft. 

All  late  machines  have  ring  armatures  (see  Figs. 
31—32),  which  are  a  great  improvement  over  the  old 
style  (spherical  armature)  in  the  way  of  better  ven- 
tilation, higher  insulation,  greater  freedom  from 
burning  out,  and  the  ease  with  which  faulty  coils 
can  be  removed  and  new  ones  substituted. 


ARMATURE   AND   FIELD-MAGNET  WINDING. 


65 


ARMATURE   AND   FIELD  MAGNET   WINDING. 


COMMUTATOR   END 


FIGURES  31  AND  32. 


AKMATURE   AND   FIELD-MAGNET   WINDING.  67 

These  armatures  are  interchangeable  with  the 
old  style  armature,  and  can  be  used  in  any  M.  D.  or 
L.  D.  machine.  The  commutator  has  only  three 
segments  in  contact  with  which  are  four  brushes. 
Regulation  is  obtained  by  an  electro-magnet  reg- 
ulator, which  controls  the  amount  of  current  by 
automatic  shifting  of  the  brushes,  in  such  a  way 
that  they  short  circuit  one  of  the  armature  coils 
for  a  greater  or  less  period  of  time  as  the  occasion 
may  require,  when  from  a  reduction  of  resistance 
in  the  lamp  circuit,  by  the  extinguishing  of  a  lamp, 
or  otherwise,  the  current  feeding  the  other  lamps 
becomes  liable  to  abnormal  increase;  this  increase 
of  current  is  made  to  flow  through  the  coils  of  wire 
surrounding  the  iron  core  of  the  regulator  magnet. 
The  core  becomes  magnetized,  causing  the  yoke 
to  which  the  brushes  are  attached  to  be  drawn  up 
towards  the  regulator  magnet  which  changes  the 
position  of  the  brushes  upon  the  commutator,  so 
that  they  draw  away  from  the  maximum  point, 
decreasing  the  potential,  when  more  lights  are 
turned  on  the  reverse  action  takes  place.  The 
current  governing  the  regulator  is  cut  in  and  out 
by  means  of  a  pair  of  electro-magnets  termed  the 
controler  magnets,  and  are  connected  with  the  reg- 
ulator magnet  of  the  dynamo. 

Sparking  at  the  commutator  is  reduced  by  a 
blower,  being  so  placed  that  it  sends  a  current  of 
air  directly  on  to  the  point  of  contact  of  the  brushes 


68  AKMATUKE    AND   FIELD-MAGNET   WINDING. 

and  the  commutator  which  blows  out  the  spark. 
The  largest  machines  have  an  electro-motive  force 
of  3000  volts,  and  will  maintain  63  arc  lights  in  a 
single  circuit. 

The  Edison  Direct  Current  Dynamo. — The  field 
magnets  consist  of  vertical  cylinders  with  large 
wrought-iron  cores,  which  rest  upon  cast-iron  pole 
pieces,  and  nearly  enclose  the  armature.  The 
armature  is  drum  shaped.  (See  Figs.  33  and  34.) 

The  core  consists  of  a  number  of  sheet-iron  discs, 
insulated  from  each  other  by  sheets  of  thin  paper. 
The  core  is  mounted  on  an  iron  shaft,  but  insulated 
from  it  by  an  interior  cylinder  of  lignum  vitae, 
while  an  external  covering  of  paper  insulates  it 
from  the  coils.  The  coils  consist  of  cotton  covered 
copper  wire,  stretched  longitudinally  and  grouped 
together  in  parallel,  a  number  of  wires  in  a  group, 
all  of  the  group  being  so  connected  as  to  form  a 
continuous  closed  circuit.  The  groups  are  ar- 
ranged in  concentric  layers,  and  are  of  the  same 
number  as  the  segments  of  the  commutator,  the 
ends  of  the  wires  in  each  group  being  attached  to 
arms  connecting  with  the  commutator  segments, 
a  spiral  arrangement  being  adopted  in  making  the 
connections  between  the  straight  portion  of  the 
wire  and  the  arms.  The  object  of  grouping  is  to 
secure  flexibility  for  winding  by  the  use  of  small 
wire  and  low  electrical  resistance,  by  having 


ABMATUKE    AND    FIELD-MAGNET   WINDING.  69 


EDISON    DIRECT  CURRENT  DYNAMO. 


70 


ARMATURE   AND   FIELD-MAGNET  WINDING. 


SPl 


ARMATUUE    AND   FIELD-MAGXET   WINDING.  71 

several  wires  in  parallel,  the  effect  as  to  the  resist- 
ance being  practically  the  same  as  if  the  several 
wires  were  combined  in  one.  At  the  ends  the 
wires  are  insulated  from  the  core  by  discs  of  vul- 
canized fibre  with  projecting  teeth.  The  discs* of 
the  core  are  bolted  together  by  insulated  rods,  and 
the  coils  are  confined  by  brass  bands  surrounding 
the  armature.  The  brushes  are  composed  of 
several  layers  of  copper  wires,  combined  with  flat 
copper  strips,  two  layers  of  wire  being  placed 
between  each  two  strips.  This  arrangement  is  to 
give  a  more  perfect  connection,  and  to  prevent 
sparking  by  furnishing  numerous  points  of  contact, 
the  copper  strips  confining  the  wire  and  making 
the  brush  more  compact. 

The  Westinghouse  Alternating  Current  Dynamo, 
for  generating  the  alternating  current,  is  repre- 
sented by  the  accompanying  illustration.  The  field 
is  composed  of  a  series  of  radial  pole  pieces  having 
alternate  polarity,  the  cores  of  which  are  cast  solid 
with  the  base  and  cap  respectively.  The  field  coils 
are  a  series  of  bobbins  each  independent  of  all  the 
others  which  are  wound  on  shells,  slipped  over  the 
pieces  and  held  up  by  bolts  at  the  periphery. 
The  bobbins  being  supplied  with  a  feeble  current 
from  the  exciter  are  of  course  subject  to  no  natural 
deterioration  and  are  not  liable  to  accident.  They 
can  only  be  damaged  by  extraneous  carelessness, 


72 


AKMATUKE    AND    FIELD- MAGNET    WINDING. 


and,  when  such  is  the  case,  the  cap  of  the  dynamo 
is  removed  and  any  bobbin  taken  out  and  replaced 
in  a  few  moments.  The  armature  is  removed  in 
the  same  manner,  as  the  whole  structure  of  the 
dynamo,  including  the  pole  pieces  and  the  bearings, 
parts  along  a  horizontal  plane  through  the  shaft. 
The  engraving  shows  the  side  of  the  dynamo 
which  carries  the  collecting  ring  ;  the  other  side 


WESTINGHOUSE  ALTERNATING    CURRENT    DYNAMO. 


has  a  similar  bearing,  beyond  which  is  an  over- 
hung pulley.  This  pulley  is  of  compressed  straw- 
board,  which  in  experience  is  found  to  exceed  all 
other  material  for  belt  traction.  The  dynamo 
rests  upon  a  cast  iron  base  and  is  adjustable  by 
means  of  a  belt  tightener.  The  dynamo  can  run 


ARMATURE   AND   FIELD-MAGNET   WINDING.  73 

in  either  direction  and  stand  either  way  around  on 
the  base.  This  of  course  adapts  it  universally  to 
any  situation. 

The  armature  is  a  structure  of  great  directness 
and  simplicity.  The  body  of  the  armature  is  of  lam- 
inated iron  plates  freely  perforated  for  ventilating 
purposes.  A  single  layer  of  wire  is  wound  in  flat 
coils  back  and  forth  across  the  face  of  the  armature 
in  a  direction  parallel  to  the  shaft,  being  retained 
by  stops  on  the  ends  of  the  armature.  Mica  and 
other  adequate  insulation  is  provided  and  the 
whole  is  wrapped  with  binding  wire.  A  ventilator 
is  attached  to  each  end  of  the  armature  and  draws 
a  strong  current  of  air  through  it. 

The  observer  will  be  struck  by  the  simplicity  of 
the  winding  on  an  alternating  current  armature  as 
compared  with  that  necessary  in  the  direct  current 
machines.  The  total  weight  of  copper  on  a  750 
light  armature  is  16  Ibs.,  disposed  in  a  single  layer, 
which  being  on  the  surface  is  readily  kept  cool, 
and  which  can  be  inspected  for  deterioration  or 
flaws  of  any  character.  A  direct  current  armature 
of  type  most  generally  in  use  of  750  lights  capacity 
on  the  other  hand  carries  more  than  10  times  this 
amount  of  wire. 

The  armatures  are  uniformly  wound  to  deliver 
1,000  volts,  and  a  higher  voltage  than  this,  for 
special  circuits,  is  obtained  by  raising  through  a 
special  converter. 


74  ARMATURE    AND    FIELD-MAGNET   WINDING. 

The  New  Multipolar  Generator, — Made  by  the 
Westinghouse  Electric  &  Manufacturing  Com- 
pany, of  Pittsburg,  Pa.,  see  illustration.  In  this 
machine  the  pole  pieces  project  radially  from  the 
interior  of  the  cylindrical  yoke  pieces,  and  by  the 
peculiar  construction  ready  access  may  be  had  to 
the  field  coils  and  armature.  The  machines  are  all 
wound  for  500  volts,  E.  M.  F.,  but  by  means  of 
a  rheostat  this  can  be  raised  to  550  or  600  volts. 
They  are  self-exciting  and  compound  wound  ma- 
chines. The  armature  is  a  distinctive  feature.  It 
is  of  the  Siemens'  type,  the  core  of  which  is  built 
up  in  the  usual  way,  of  a  large  number  of  thin  iron 
discs  which  are  rigidly  keyed  to  the  shaft.  The 
wires  are  not  placed  on  the  exterior  of  the  core,  as 
is  usually  done,  but  are  placed  in  insulating  tubes 
which  are  embedded  in  the  iron  of  the  core.  This 
construction  obviates  the  use  of  binding  wires.  A 
special  method  of  winding  is  used,  and  the  amount 
of  wire  necessary  is  reduced  to  a  minimum.  The 
commutators  are  long  and  massive.  The  brush 
holders  are  composed  of  independent  holders,  thus 
allowing  each  carbon  brush  to  be  removed  without 
disturbing  the  others.  The  machine  is  carefully 
regulated,  designed  for  railway  use  and  to  require 
a  minimum  amount  of  attention. 


AKMATURE   AND   FIELD-MAGNET  WINDING.  75 


WESTINGHOUSE    MULTIPOLAR   GENERATOR. 


76  ARMATURE   AND   FIELD-MAGNET   WINDING. 


CHAPTER  IX. 


MOTORS. 

THE  dynamo  generates  electricity,  and  is  driven 
by  mechanical  means.  The  electric  motor  fur- 
nishes power,  and  is  actuated  by  electricity  gene- 
rated from  a  dynamo  or  an  electric  battery.  The 
field  winding  of  a  motor  is  adapted  to  the  work, 
which  it  is  to  perform.  Series  winding  is  used 
when  a  variable  speed  is  required  and  where  the 
regulation  may  be  attended  to  by  hand,  its  chief 
advantage  being  in  its  great  starting  power.  Shunt 
winding  is  used  where  constant  speed  is  required. 
Compound  winding  is  theoretically  more  correct, 
but  a  shunt  winding  will  regulate  the  machine 
closely  enough  for  all  practical  purposes,  and  is 
the  one  most  commonly  used.  A  brief  description 
of  some  of  the  machines  manufactured  by  the  lead- 
ing electrical  companies  will  give  the  reader 
a  general  understanding  of  their  different  styles 
of  mechanical  and  electrical  construction. 

The  Crocker-Wheeler  Electric  Motor,  of  which 
two  illustrations  are  given,  on  pages  78  and  80, 


ARMATURE    AND   FIELD-MAGNET   WINDING.  77 

possess  some  special  features  of  merit  which  are 
as  follows  : 

The  field  magnets  are  composed  entirely  of  the 
best  wrought-iron,  each  magnet  being  forged  in  a 
single  piece,  and  set  deeply  into  the  base  in  order 
to  secure  solidity  and  ample  magnetic  contact. 
The  space  for  wire  on  these  magnets  is  perfectly 
cylindrical,  in  the  form  of  an  ordinary  spool,  there- 
by insuring  smooth  and  perfect  winding  of  the 
wire,  and  is  short  in  length,  permitting  the  shaft 
of  the  machine  to  be  low  enough  to  free  it  from 
vibration.  By  this  construction  the  neutrality  or 
freedom  of  the  base  from  magnetism  is  secured, 
and  there  is  no  tendency  to  leakage.  This  is 
claimed  to  make  the  machine  much  superior  to 
those  in  which  the  base  is  made  to  serve  as  one  of 
the  pole  pieces,  as  the  bearings  then  become  mag- 
netized and  make  the  shaft  bind. 

The  armatures  contain  several  improvements. 
They  are  sufficiently  large  in  diameter  to  obtain 
slow  speed,  and  are  so  designed  that  the  wire 
winding  is  entirely  embedded  below  the  surface  of 
the  iron  core,  thus  protecting  it  from  all  injury, 
holding  it  rigidly  in  position,  and  rendering  it 
possible  for  the  magnets  to  approach  very  closely 
to  the  core,  so  that  an  intense  magnetic  effect  is 
produced.  The  armature  is  mounted  upon  a  brass 
face-plate,  which  is  first  turned  perfectly  true,  and 
after  completion  the  armature  is  very  carefully 


78  ARMATURE   AND    FIELD-MAGNET  WINDING. 


CROCKER-WHEELER   ELECTRIC    MOTOR. 


ARMATURE    AND   FIELD -MAGNET   WINDING.  79 

balanced,  so  that  when  run  at  full  speed  the  motion 
is  hardly  perceptible. 

The  bearings  are  all  of  the  self -oiling  type,  which 
do  not  require  attention  oftener  than  once  in  two 
to  four  weeks. 

The  base  of  the  pillow-block  is  hollow,  and  con- 
tains a  supply  of  oil,  which  is  carried  over  the  shaft 
by  two  rings  which  travel  upon  the  latter,  and  are 
caused  to  revolve  by  its  motion.  They  dip  in  the 
oil  and  carry  it  continuously  to  the  upper  side  of 
the  shaft. 

The  bushings  in  which  the  shaft  runs  Vest  in  turn 
in  universal  or  ball  joints  in  seats  of  babbit  metal 
in  pillow-blocks,  so  that  the  bearings  are  sure  to 
assume  perfect  alignment  when  the  shaft  is  intro- 
duced. After  the  motor  has  run  a  month,  the 
old  oil  containing  the  grit,  etc.,  [should  be  drawn 
off  from  the  pet  cock  at  the  base  of  the  pillow 
block.  This  cock  should  then  be  closed  and  fresh 
oil  introduced  by  removing  the  thumb  screw  in 
the  pillow  block  cap  on  top. 

The  brushes  are  held  by  rocker  arms  which  can 
revolve  freely  around  the  entire  circle,  without  fear 
of  the  brass  connecting  parts  "grounding"  against 
the  frame,  a  great  advantage  in  special  work  where 
motors  are  to  be  adapted  for  use  in  unusual  positions. 

With  this  form  of  armature  core  which  reaches 
close  to  the  field  magnets,  and  the  high  grade  of 
wrought-iron  used  for  the  latter,  it  is  claimed  they 


80  ARMATURE    AND   FIELD-MAGNET   WINDING. 


SKELETON     VIEW,       SHOWING       INTERNAL       CONSTRUCTION       OF 
CROCKER-WHEELER    ELECTRIC    MOTOR. 


ARMATURE   AND   FIELD-MAGNET  WINDING.  81 

are  enabled  to  maintain  the  magnetism  and  there- 
fore the  power  of  these  motors,  with  only  about 
one-third  as  much  wire  as  is  used  on  the  fields  of 
ordinary  standard  machines.  This  great  saving  of 
wire  not  only  reduces  the  weight  of  the  machine, 
but  materially  increases  its  efficiency,  or  the  amount 
of  power  that  can  be  obtained  from  a  given  amount 
of  electricity,  for  with  less  wire  less  electricity  is 
required. 

The  speed  of  motors  is  very  low,  which  in  many 
cases  makes  counter-shafting,  etc.,  unnecessary. 

The  proximity  of  the  armature  core  to  the  field 
magnets  renders  a  high  magnetic  pressure  un- 
necessary, therefore  the  magnetism  escaping  from 
the  fields  is  very  much  reduced. 

Double  insulated  wire  is  used  throughout  for  the 
windings,  the  cores  being  first  wrapped  with  oiled 
paper  and  heavy  canvas  saturated  with  shellac. 

The  rocker  arm  is  provided  with  a  heavy  insula- 
ted handle  to  enable  all  adjustments  to  be  made 
without  touching  the  conducting  parts,  and  the  en- 
tire machine  is  heavily  japaned  and  baked  at  a  high 
temperature,  thus  securing  a  polished  surface  which 
resists  dirt  and  oil. 

In  connection  with  their  incandescent  motors, 
they  furnish  fire-proof  and  indestructible  regulating 
boxes  or  rheostats  for  starting,  stopping  and  vary- 
ing the  speed  of  the  machines.  These  are  built 
entirely  of  slate,  china  and  iron.  The  arrangement 


82  AKMATURE   AND    FIELD-MAGNET   WINDING. 

of  contacts  in  the  switch  on  top  of  the  regulator 
is  such  that  both  the  field  and  armature  of  the  mo- 
tor are  charged  by  the  single  operation  of  turning 
the  knob,  making  it  impossible  to  put  the  current 
on  the  armature  before  the  field  is  charged,  which 
has  so  often  been  the  cause  of  the  accidental  burn- 
ing out  of  many  motors  by  the  use  of  ordinary 
regulators. 

The  field  is  first  charged  through  a  small  resist- 
ance coil  which  is  put  in  for  the  purpose  of  prevent- 
ing a  too  sudden  change  in  the  magnetic  strength 
of  the  latter,  as  well  as  to  divide  the  spark  when 
the  motor  is  disconnected.  The  coils  used  for  start- 
ing the  armature  are  all  of  the  same  size  wire 
carefully  tried  for  carrying  the  full  current  of  the 
machine  at  all  speeds.  With  the  fire-proof  regu- 
lator, the  motor  can  therefore  be  slowed  down  and 
left  running  at  any  desired  speed,  indefinitely,  and 
the  usual  caution  "never  to  leave  the  box  half  turned 
on  for  fear  of  overheating  and  fire"  is  unnecessary. 

The  Thomson-Houston  Stationary  Motor. — The 
15  horse-power  motor  shown  in  the  illustration  on 
next  page  has  an  average  commercial  efficiency 
when  fully  loaded  of  91  per  cent.  This  high  effi- 
ciency is  obtained  by  paying  careful  attention  to 
the  electric  and  magnetic  proportioning  of  the 
motor. 

The  magnetic  circuit  is  very  short  and  of  ample 


ARMATURE   AND   FIELD-MAGNET  WINDING.  83 


THOMSON-HOUSTON     STATIONARY    MOTOR. 


84  ARMATURE   AND   FIELD-MAGNET   WINDING. 

section,  and  therefore  of  low  resistance,  and  the 
magnetic  poles  are  so  formed  as  to  convey  the  mag- 
netism into  the  armature  with  the  least  possible 
loss.  As  will  be  noted  in  the  engraving,  the  poles 
of  the  field-magnets,  the  bodies  or  cores  of  which 
are  round  in  section,  project  upward,  enclosing  the 
armature.  The  armature  is  nearly  square  in  long- 
itudinal section  and  relatively  large  in  diameter. 

This  gives  a  high  peripheral  velocity  and  a.  rapid 
cutting  of  the  lines  of  force.  In  consequence  of 
this  construction,  also,  the  armature  is  capable  of 
exerting  a  powerful  rotative  force.  The  armature 
being  short,  avoids  the  use  of  a  long  and  conse- 
quently less  rigid  shaft.  The  coils  of  the  motor- 
magnet  are  wound  on  bobbins  which  are  slipped 
over  the  cores ;  it  is  therefore  easy  to  change  a 
coil  or  to  replace  it  for  any  purpose  whatever. 

The  field  is  wound  in  shunt  to  the  armature,  and 
is  relatively  of  a  very  high  resistance. 

This  reduces  the  amount  of  electrical  energy  re- 
quired to  energize  the  field-magnet  to  a  very  small 
fraction  of  the  total  electrical  energy  absorbed  by 
the  motor.  The  armature  bore  is  thoroughly  well 
built  and  is  a  very  solid  and  substantial  structure. 

At  the  same  time  the  perfect  lamination  of  the 
core  reduces  the  loss  by  Foucault  currents  to  a 
small  amount. 

The  winding  on  the  armature,  which  is  a  modifi- 


ARMATURE   AND   FIELD-MAGNET   WINDING.  85 

cation  of  the  well-known  Siemens'  type,  is  of  very 
low  resistance. 

The  copper  wire  on  the  armature  is  held  in  place 
by  means  of  bands,  which  are  made  of  such  strength 
that  it  is  impossible  for  them  to  yield  from  the 
centrifugal  force,  even  when  the  motors  are  run  at 
abnormal  speed. 

The  Ford  &  Washburn  Electric  Motor  oi  Cleveland, 
is  shown  in  the  illustration.  The  special  improve- 
ment, they  claim,  puts  their  motor  far  in  advance 
of  many  others  and  places  the  use  of  electricity  for 
lighting  within  the  reach  of  the  smallest  plants,  is 
its  self-ventilating  feature ;  but  the  motor  itself 
possesses  many  points  of  superiority.  The  bed 
plates  and  brackets  are  one  complete  casting. 

The  magnet  yokes  are  wrought  iron  fastened  to 
the  bed  plate,  and  the  pole  pieces  are  separate  cast- 
ings bolted  to  magnet  yokes.  The  field  cores  are 
wound  on  separate  shells,  and  are  interchangeable 
for  all  machines  of  same  size.  The  armature  shaft 
is  steel  and  of  extra  large  size. 

The  especial  feature  of  their  motor,  as  above 
stated,  is  the  armature,  which  is  self-ventilating. 

It  draws  a  current  of  air  from  both  ends  and 
along  the  line  of  shaft  and  out  through  the  discs,, 
which  are  separated,  and  through  the  winding,  with 
openings  to  let  the  air  pass  out.  The  rapid  rotary 
motion  of  the  armature  sends  out  the  current  of  air,. 


ARMATURE   AXD   FIELD-MAGXET   WIXIHXG. 


FIG.  35. 


FIG.  36. 


ARMATURE    AND   FIELD-MAGNET   WINDING.  87 

which  keeps  the  armature  and  pole  pieces  cool  and 
therefore  more  effective  than  the  old  style  which 
is  so  liable  to  heat  up.  This  self- ventilating  feature 
it  is  claimed,  is  found  in  no  other  motor  at  present 
manufactured.  It  is  adapted  to  both  motors  and 
dynamos.  Fig.  35  shows  the  motor;  Fig.  36  shows 
the  armature. 

The  Neiv  Mather  Motors  and  Power  Generators. 
— Recognizing  the  demand  for  power  transmission 
by  means  of  electric  current,  the  Mather  Electric 
Company  has  bought  out  a  series  of  machines  for 
that  purpose,  which,  while  embodying  the  essential 
features  of  the  well-known  Gramme  ring  type,  can 
be  more  readily  insulated  against  the  high  potentials 
required  for  power  service. 

One  of  the  essential  features  of  the  old  type  of 
Mather  machines  was  a  field  magnet  having  the 
form  approximately  of  the  magnetic  lines  of  force 
and  consisting  of  one  piece.  In  the  new  type  the 
cores  of  the  field  magnet  are  straight,  permitting 
the  use  of  coils  of  wire  that  can  be  wound  separate- 
ly on  a  machine,  while  the  rest  of  the  magnetic 
circuit  is  practically  a  ring,  and  the  whole,  includ- 
ing the  cores  and  pole  pieces,  is  cast  in  one  piece 
without  a  joint. 

The  motors  are  built  in  sizes  of  I,  3,  6  and  10 
h.  p.  with  two  poles  and  20,  30  and  40  h.  p.  with 
four  poles.  The  generators  are  built  up  to  30,000, 


88  ARMATURE   AND   FIELD-MAGNET  WINDING. 


NEW    MATHER    MOTOR. 


ARMATURE    AND    FIELD-MAGNET   WINDING.  89 

50,000  and  75,000  watts  with  four  poles,  and  180,- 
ooo  watts  with  six  poles.  Drum  armatures  are  used 
in  all  the  machines.  In  the  four-pole  machines  the 
winding  is  such  that  the  current -has  but  two  paths 
through  the  armature  wires,  and  by  a  special  meth- 
od, devised  by  Prof.  Anthony,  no  two  wires  having 
any  great  difference  of  potential  are  brought  near 
each  other. 

The  illustration  represents  the  /5,ooo-watt  gen- 
erator, with  the  field  magnet  in  one  casting.  In 
the  i8o,ooo-watt  six-pole  machine  the  field  magnet 
is  cast  in  two  halves,  but  divided  through  the  mid- 
dle of  two  opposite  poles  instead  of  across  the  mag- 
netic circuit.  The  small  motors  are  wound  and 
kept  in  stock  for  220  volts,  but  can  easily  be  wound 
for  no  or  500  volts,  when  desired.  The  winding 
is  such  that  in  no  case  is  there  a  loss  in  the  arma- 
ture of  more  than  four  per  cent,  and  the  speeds  run 
from  1,500  revolutions  for  the  10  h.  p.  to  2,500  for 
the  i  h.  p.  The  variation  in  speed  from  full  load 
to  no  load  is  never  more  than  four  per  cent. 

TJie  Thomson-Houston  W.  P.  Raihvay  Motor. — 
The  following  description  was  taken  from  the 
Electrical  World: 

One  of  the  most  interesting  exhibits  at  the  Pitts- 
burgh Street  Railway  Convention  was  a  new  slow 
speed  railway  motor  of  the  Thomson-Houston  com- 
pany, of  which  the  accompanying  illustrations  give 


90  AKMATUKE    AND   FIELD-MAGNET   WINDING. 

an  excellent  idea.  It  has  been  in  process  of  evolu- 
tion for  six  months  or  more  and  has  been  worked  up 
under  the  careful  superintendence  of  Mr.  Walter 
Knight.  The  new  machine  embodies  some  decided- 
ly novel  features  acnd  its  excellent  performance  on 
the  special  car  equipped  with  it  was  very  favorably 
commented  upon.  It  is  known  to  the  trade  a's  the 
W.  P.  motor,  which  being  interpreted  means  water- 
proof, and  it  well  deserves  the  name,  because  of 
the  particularly  complete  iron-clad  character  of  the 
field  magnets. 

Fig.  37  gives  a  perspective  view  of  the  motor, 
and  from  it  the  arrangement  of  the  iron  is  at  once 
obvious.  Singularly  enough,  it  is  a  two-pole  machine 
so  arranged  on  the  theory  that  the  comparatively 
slight  gain  in  weight  efficiency  that  could  be  ob- 
tained with  a  mutipolar  type  is  more  than  offset  by 
the  increased  complication  of  the  windings.  The 
only  portions  of  the  machine  open  to  the  outside 
air  are  exposed  at  the  two  oval  openings  at  the  ends 
of  the  armature  shaft,  and  even  these  can  be  easily 
fitted  with  covers  should  such  a  course  prove  de- 
sirable. The  whole  magnetic  circuit  is  composed 
of  two  castings  bolted  together  and  free  to  swing 
apart  by  a  hinge  allowing  ready  access  to  the  ar- 
mature. 

Fig.  38  gives  an  excellent  idea  of  the  internal 
arrangements.  The  armature  itself  is  very  nearly 
twenty  inches  in  diameter,  a  very  powerful  Pacinotti 


A.K.MATUBE    AXI>   FIELD-MAGNET  WINDING.  91 


FIG.  37. 


FIG.  38. 


92  ARMATURE   AND    FIELD-MAGNET   WINDING. 

ring  nearly  six  inches  on  the  face  and  of  about  the 
same  depth.  It  is  wound  with  comparatively  coarse 
wire  in  sixty-four  sections,  with  fourteen  turns  to 
the  section.  Each  coil  is  tightly  placed  in  the 
space  between  two  of  the  projecting  teeth,  and 
about  the  interior  space  the  separate  coils  are 
closely  packed,  leaving  only  sufficient  room  for  the 
four-armed  driving  spider. 

As  will  be  seen,  the  armature  takes  up  most  of 
the  full  height  of  the  machine,  the  pole  pieces  be- 
ing but  trifling  projections  and  the  requisite  cross- 
section  of  iron  being  obtained  by  extending  the 
poles  to  form  a  closely  fitting  iron  box  that  appears 
in  the  exterior  view.  An  unusual  feature  is  the 
use  of  but  a  single  magnetizing  coil  wound  not  di- 
rectly about  the  upper  pole  piece  but  on  the  casing 
immediately  surrounding  it.  The  lower  pole  is  but 
slightly  raised  and  both  pole  pieces  are  of  the 
greatest  extent  permissible  with  the  dimensions  of 
the  machine.  The  use  of  a  single  magnetizing 
coil  produces  naturally  an  unbalanced  field  and  a 
strong  upward  pull  on  the  armature  tending  to  re- 
lieve the  pressure  on  the  bearings.  The  iron-clad 
form,  however,  tends  to  distribute  the  lines  of 
force  so  as  to  avoid  the  sparking  and  change  of 
lead  that  might  otherwise  have  to  be  feared.  The 
single  coil  is  wound  with  quite  coarse  wire  and  its 
position  insures  the  maximum  magnetic  effect 
from  the  current. 


ARMATURE    AND    FIELD-MAGNET   WINDING.  93 

The  speed  of  the  new  motor  is  about  the  same 
as  that  of  the  older  S.  R.  G.  form,  but  its  general 
working  efficiency  is  somewhat  better,  owing  not 
so  much  to  a  greater  maximum  of  efficiency  as  to 
a  better  working  curve — at  both  heavy  and  light 
loads.  The  brush  holders  are  shown  in  the  cut, 
and  the  slots  in  which  they  fit  render  their  position 
evident.  The  brushes  are  of  the  ordinary  carbon 
description  and  are  readily  accessible  through  the 
opening  at  the  end  of  the  shaft. 

In  operation  the  W.  P.  motor  has  been  highly 
satisfactory.  It  runs  with  but  trifling  sparking  and 
no  heating  to  speak  of,  gives  a  very  powerful 
torque,  and  is  singularly  free  from  liability  to  dam- 
age of  the  armature,  for  which  its  careful  insula- 
tion and  the  Pacinotti  form  adopted  are  responsi- 
ble. It  is  now  being  regularly  manufactured  at  the 
Thomson-Houston  works,  and  it  is  expected  to 
take  with  great  advantage  the  place  in  popular  fa- 
vor of  the  S.  R.  G,  motor  that  has  made  so  good  a 
reputation  for  itself  during  the  past  summer.  It  is 
an  interesting  departure,  both  electrically  and  me- 
chanically, and  aside  from  its  special  features  its 
general  qualities  of  iron-clad  field,  gears  running 
in  oil,  and  the  ease  of  access  to  the  working  parts 
will  commend  it  to  the  practical  street  railway 
man. 

TJie  Porter  Electric  Motor  is  shown  by  the  ac- 
companying engraving.  It  is  an  extremely  effi- 


94  ARMATURE   AND   FIELD-MAGNET  WINDING. 


PORTER    ELECTRIC    MOTOR. 


ARMATURE   AND   FIELD-MAGNET   WINDING.  95 

cient  battery  motor  and  is  very  simple  in  its  con- 
struction. It  has  but  one  field  winding  and  its 
armature  is  of  the  Siemens  type. 

Three  sizes  are  made,  viz.,  No.  I,  52  h.  p.  No. 
2,  ^  h.  p.,  and  No.  3,  ^  The  No.  3,  or  largest 
size,  will  run  a  6-inch  ventilating  fan  or  a  family 
sewing  machine.  It  has  no  dead  centre  and  there- 
fore starts  instantly  upon  the  application  of  the 
current,  which  may  be  furnished  by  a  storage  cell 
or  a  bicromate  battery.  The  Taylor  battery  will 
be  found  an  excellent  battery  for  running  this  ma- 
chine when  one  does  not  wish  to  use  a  storage 
cell. 

The  No.  3  motor  weighs  six  pounds.  Is  5^ 
inches  long,  4^  inches  high  and  4^  inches  wide. 

The  Ferret  Motor. — The  chief  distinctive  feature 
of  this  machine  is  the  lamination  of  the  field  mag- 
net. Instead  of  casting  or  forging  this  in  several 
solid  pieces,  as  is  usually  done,  it  is  built  of  thin 
plates  of  soft  charcoal  iron,  which  are  stamped  di- 
rectly to  their  finished  form  and  clamped  together 
by  bolts  in  such  a  manner  as  to  secure  great  me- 
chanical strength. 

The  advantages  of  such  a  construction  are,  in 
brief,  a  magnetic  field  of  great  intensity  and  the 
entire  prevention  of  all  wasteful  induced  currents 
in  magnets  and  pole-pieces. 

The  armature  core   is  also  laminated,  and   the 


ARMATURE    AND    FIKI.D-M AftNET   WINDING. 


THE    FERRET    MOTOR. 


ARMATUIIE    AND   FIELD-MAGNET   WINDING.  97 

plates  have  teeth,  which  form  longitudinal  chan- 
nels on  its  periphery,  in  which  the  coils  are  wound. 

The  plates  in  both  field  and  armature  are  in  the 
same  plane,  and  are  of  soft  charcoal  iron,  with  its 
grain  running  in  the  direction  of  the  line  of  mag- 
netic force,  and  there  is  the  least  possible  break  in 
the  continuity  of  the  circuit,  there  being  no  air 
gap  between  the  iron  of  the  field  and  the  iron 
teeth  of  armature,  except  that  required  for  clear- 
ance in  rotation.  Thus  we  have  a  magnetic  circuit 
of  lowest  possible  resistance,  and  it  follows  from 
well-known  laws  that  we  secure  the  maximum  of 
effective  magnetism  with  a  minimum  expenditure 
of  magnetizing  power. 

The  armature  coils  being  practically  imbedded 
in  the  armature,  receive  the  highest  inductive  ef- 
fect from  the  intensely  magnetized  iron.  * 

The  high  efficiency  which  such  construction 
should  give  theoretically  is  practically  demon- 
strated by  the  machines  in  actual  work,  and  ranges 
from  70^)  in  the  smaller  to  93^  in  the  larger. 

Attempts  have  been  made  by  many  since  the 
days  of  Pacinotti  to  use  toothed  armatures,  but 
with  the  result  that  very  troublesome  and  wasteful 
heating  effects  were  produced  in  the  solid  magnets 
and  pole  pieces  commonly  used.  With  laminated 
field  magnets  these  disadvantages  are  avoided,  and 
we  are  able  to  secure  the  advantages  enumerated, 
as  well  as  others,  among  which  may  be  mentioned 


98 


ARMATUKE    AND    FIELD-MAGNKT   WI.VDING. 


FIG.  39. 


ARMATURE   AND    FIELD-MAGNET  WINDING.  99 

the  important  ones,  positive  driving  of  the  arma- 
ture coils  and  less  liability  of  winding  out  of  bal- 
ance. 

It  will  be  seen  that  the  armature  is  a  ring  of 
comparatively  large  diameter,  with  longitudinal 
channels  on  its  periphery,  in  which  the  conductors 
are  wound,  and  thus  embedded  in  the  iron,  which 
is  in  such  close  proximity  to  the  iron  pole  pieces 
that  there  is  practically  no  gap  in  the  magnetic 
circuit. 

The  field  consists  of  three  separate  magnets 
arranged  at  equal  distances  around  the  armature, 
each  magnet  having  two  pole  pieces.  See  Fig.  39. 
The  winding  is  such  as  to  produce  alternate  North 
and  South  poles.  The  magnets  are  built  up  of 
plates  of  soft  charcoal  iron,  which  are  shaped  as 
shown  in  the  diagram,  and  the  magnet  thus  pro- 
duced is  of  such  a  form  that  it  may  be  readily 
wound  in  a  lathe.  A  non-magnetic  bolt  passes 
through  a  hole  in  each  pole  piece  and  the  plates 
are  clamped  together  between  washers  and  nuts  on 
the  same.  These  bolts  also  serve  to  attach  the 
magnets  to  the  two  iron  end  frames,  which  are  of 
ring  shape  and  are  bolted  to  the  bed  plates  of  the 
machine. 

The  magnetic  circuit  is  of  unusally  low  resist- 
ance by  reason  of  its  shape,  its  shortness,  which  is 
shown  by  the  diagram,  and  the  superior  quality  of 
iron  used. 


100  ARMATURE   AND   FIELD-MAGNET   WINDING. 

There  is  no  magnetism  whatever  in  the  frame, 
bed  or  shaft  of  the  machine,  as  the  magnets  are 
supported  at  some  distance  from  the  frame  by 
means  of  the  non-magnetic  bolts,  and  the  armature 
is  mounted  on  the  shaft  by  spiders  of  non-mag- 
netic metal. 

There  is  therefore  no  opportunity  for  magnetic 
leakage,  and,  furthermore,  the  whole  is  enclosed 
by  a  shield  or  case  of  sheet  metal,  as  shown  in  the 
illustration  on  page  96. 

The  practical  advantages  of  low  speed  machines 
are  many.  For  instance,  in  ordinary  machine 
shops,  wood-work  shops,  printing  offices,  etc.,  the 
shaft  is  commonly  run  200  to  300  revolutions  per 
minute,  and  it  is  a  simple  matter  to  belt  direct  to 
it  from  a  motor  running  500  to  600  revolutions, 
thus  saving  the  first  cost  of  a  counter-shaft  and 
one  belt)  and  saving,  also,  considerable  power 
which  would  be  lost  in  transmitting  through  the 
counter-shaft  and  additional  belt,  which  would  be 
used  necessarily  with  a  motor  of  high  speed.  The 
advantage  is  equally  as  great  in  case  of  elevators 
operated  by  a  belt  from  the  motor,  and  indeed,  it 
is  possible  to  gear  direct  from  the  motor  to  the 
elevator. 

The  Excelsior  Motor. — The  engraving  on  page 
101  illustrates  the  arc  light  circuit  or  constant  cur- 
rent motor  of  the  Excelsior  Electric  Co.  This 


ARMATTJKE    AND   FIELD-MAGNET    WINDING.  101 


THE   EXCELSIOR    MOTOR. 


102  ARMATURE    AXD    FIELD-MAGXET    WINDING. 

motor  has  its  armature  and  field-magnet  coils  con- 
nected in  series.  As  it  is  supplied  with  current  by 
a  generator  whose  electro-motive  force  is  varied  by 
an  automatic  regulator  to  suit  the  demands  of  the 
motors  on  its  circuit,  it  would  run  at  a  constantly 
increasing  speed,  when  lightly  loaded,  were  it  not 
regulated  and  the  speed  kept  uniform  by  a  govern- 
ing device.  This  consists  of  a  centrifugal  gov- 
ernor which  controls  the  strength  of  the  field-mag- 
nets by  cutting  out  the  successive  layers  of  wire 
in  the  coils  as  the  load  decreases,  and  cutting  them 
in  when  it  increases. 

The  two  main  bearings  of  the  motor-shaft  and 
the  ball  and  socket  bearings  of  the  governor  are 
provided  with  oil  chambers,  from  which  the  oil  is 
led  to  the  wearing  surfaces  by  means  of  felt  strips. 

The  Wightman  Single-Reduction  Railway  Motor. 
— Among  the  very  first  to  recognize  the  desira- 
bility of  as  well  as  the  possibility  of  eliminating 
one  set  of  transmission  gears  in  electric  street 
railway  cars  was  Mr.  Merle  J.  Wightman,  who,  as 
electrician  of  the  Wightman  Electric  Manufactur- 
ing Co.,  of  Scranton,  Pa.,  over  a  year  ago  com- 
menced experiments  towards  the  development  of  a 
slow-speed  single-reduction  motor.  The  results  of 
this  work  are  embodied  in  the  motor  shown  in  the 
accompanying  engraving,  Fig.  40,  from  which 
it  will  be  seen  that  the  "  Kennedy"  type 


AHMATUISK    AM)    FI1- I.D-MAGXtT    WINDING. 


103 


104  ARMATURE    AND   FIELD-MAGNET    WINDING. 

of  field-magnet  is  employed.  This  form  of  field- 
magnet  has  the  advantage  of  almost  completely 
covering  the  field  coils  and  producing  an  "iron 
clad"  moton  It  gives  a  very  strong  and  efficient 
field  and  all  four  poles  are  excited  by  two  field 
windings. 

The  armature  is  of  the  Gramme  type,  and  the 
commutator  is  cross-connected  so  that  but  two 
brushes  are  used,  placed  at  an  angle  of  90  degrees 
and  on  top  of  the  commutator. 

The  cross-connecting  of  the  commutator  is  ac- 
complished in  a  remarkably  simple  way.  All  the 
crossing  cables  are  formed  symmetrically  into  a 
flat  disc  which  is  firmly  bolted  to  the  head  of  the 
commutator  and  becomes  an  integral  part  of  it.  In 
this  way  all  possibility  of  vibration  and  risk  of 
breakage  is  overcome.  The  commutator  lead-wires 
are  all  of  flexible  cable,  after  the  Wightman  Com- 
pany's well-known  method  of  armature  winding. 
These  lead-wires  are  fastened  to  the  commutator 
without  screws  and  in  such  a  way  that  they  can  be 
detached  in  a  few  minutes,  when  it  becomes  neces- 
sary to  remove  a  commutator.  The  armature  is 
mounted  within  a  strong,  continuous  frame  form- 
ing part  of  the  field  magnets.  The  bearings  are 
self -oiling  and  dust-proof,  and  are  designed  to  be 
used  with  grease,  oil,  or  both. 

Either  field  winding  is  removable  without  dis- 
turbing the  other  or  the  armature,  each  winding 


ABMATUKE   AND   FIELD  MAGNET   WINDING.  105 


FlG.     41.— FIELD   WINDING   OF   WIGHTMAN   SINGLE 
REDUCTION    RAILWAY    MOTOR. 


ARMATURE  OF  WIGHTMAN   SINGLE  REDUCTION 
RAILWAY    MOTOR. 


106  ARMATURE   AND   FIELD- MAGNET   WINDING. 

being  made  up  of  separate  coils,  one  of  which  is 
shown  in  Fig  41.  The  removal  of  two  bolts  at  one 
end  makes  it  possible  to  lift  out  one  of  the  fields, 
after  which  the  armature  can  be  taken  out.  The 
top  field  pole  is  hinged  at  one  end  for  convenience 
in  removing  the  fields  or  armature. 

The  ratio  of  the  reduction  of  the  gearing  is  4.4 
to  i,  the  armature  pinion  having  fifteen  teeth  and 
a  diameter  of  five  inches.  This  ratio  gives  about 
480  revolutions  of  the  armature  at  a  car-speed  of 
10  miles  an  hour. 

The  aim  of  the  designer  of  the  Wightman  mo- 
tor has  been  to  attain  as  great  an  efficiency  as  pos- 
sible with  the  wide  variation  of  speed  and  load  met 
with  in  street  railway  practice.  This  has  been  ob- 
tained by  means  of  large  field  magnets  of  a  great 
number  of  turns  of  wire.  In  fact,  speed  regula- 
tion is  obtained  without  the  use  of  any  external 
resistance  above  three  or  four  miles  an  hour.  On  a 
level,  cars  equipped  with  two  2O-h.  p.  Wightman 
motors  have  frequently  attained  a  speed  above 
twenty-five  miles  an  hour. 

Mr.  Wightman's  experience  has  led  him  to  the 
belief  that  there  is  no  economy  in  operating  mo- 
tors of  small  capacity.  Many  roads  are  operated 
in  such  a  way  that  cars  are  barely  maintained  on 
schedule  time  by  dangerous  and  reckless  running 
on  down  grades.  A  little  calculation  will  show 
that  by  the  expenditure  of  a  little  more  power, 


ARMATURE    AND    FIELD-MAGNET  WINDING.  107 

grades  may  be  climbed  rapidly,  and  as  a  result, 
much  more  service  can  be  gotten  from  a  given  ex- 
penditure in  wages  for  conductors  and  motor-men 
and  interest  on  plant ;  and  the  cost  of  the  extra 
coal  will  be  comparatively  insignificant.  It  is 
much  safer  to  climb  grades  rapidly  rather  than  to 
descend  them  at  a  high  rate  of  speed,  not  to  men- 
tion the  greater  satisfaction  of  patrons.  When 
climbing  a  grade  a  stoppage  of  power  and  applica- 
tion of  brakes  will  bring  a  car  to  a  standstill  within 
surprisingly  short  distance.  Since  the  wear  and 
tear  of  ample-sized  motors  is  obviously  less  than 
those  overworked,  all  consideration  of  economy 
and  safety  would  therefore  point  to  the  use  of  the 
former. 

While  in  the  Wightman  motor  electrical  per- 
fection has  not  been  sought  for  at  the  expense  of 
simplicity  and  durability,  a  very  high  efficiency  is 
obtained.  The  armature  resistance  of  the  20  h.  p. 
motor  is  .75  ohm,  and  that  of  the  main  field  coils 
.15  ohm,  with  a  load  of  40  amperes,  or  over  26 
electrical  horse  power  ;  this  would  give  a  loss  of 
potential  in  the  motor  of  36  volts,  or  an  electrical 
efficiency  of  92.8.  Even  with  this  excessive  load 
the  commercial  efficiency  has  been  found  to  be  as 
high  as  87  per  cent.  The  large  field,  referred  to 
above,  makes  possible  a  high  efficiency  at  low 
speed  and  light  loads.  These  qualities  are  synony- 
mous with  powerful  torque  or  starting  force. 
A  loaded  car  equipped  with  Wightman  motors 
requires  not  more  than  from  15  to  20  amperes  to 
start  on  a  level. 


108  ARMATURE   AND   FIELD-MAGNET  WINDING. 

APPENDIX  A. 

ELECTRICAL  AND  MAGNETIC  UNITS. 

AMPERE. — The  unit  of  current  strength.  It  is 
the  flow  of  electricity  produced  by  the  pressure 
of  one  volt  on  a  resistance  of  one  ohm. 

COULOMB.— The  unit  of  electric  quantity.  It 
is  the  amount  of  electricity  which  flows  past  a 
given  point  in  one  second  on  a  circuit  conveying 
one  ampere. 

FARAD. — The  unit  of  capacity.  A  condenser 
that  will  hold  one  coulomb  at  a  pressure  of  one 
volt  has  a  capacity  of  one  farad. 

OHM. — The  unit  of  electrical  resistance.  Ohms 
law  states  that  the  current  in  any  circuit  is 
equal  to  the  E.  M.  F.  acting  on  it  divided  by  its 
resistance. 

VOLT. — The  unit  of  electro-motive  force  or  pres- 
sure analogous  to  the  head  of  water  in  hy- 
draulics. 


ARMATURE   AND   FIELD-MAGNET  WINDING.  109 

WATT.— The  unit  of  work.  ^  of  a  horse 
power,  i.e.  746  Watts  equal  i  horse  power.  We 
may  find  the  Watts  used  in  a  circuit  by  three 
formulae,  thus : 

Watts=Amperes  (squared)  X  ohms.  • 
Watts=Amperes  X  volts. 
Watts=Volts  (squared)  -4-  by  ohms. 

DYNE. — The  absolute  unit  of  force.  It  is  that 
force  which  if  it  acts  on  one  gramme  for  one 
second  gives  to  it  a  velocity  of  one  centimetre 
per  second.  In  the  *C.  G.  S.  system  the  unit 
of  magnetism  is  the  force  of  a  magnetic  pole, 
which  repels  an  equal  pole  at  the  distance  of 
one  centimetre  with  a  force  of  one  dvne. 


*C.  G.  S. — The  abbreviation  of  centimetre,  gramme,  second, 
and  used  to  designate  the  so-called  absolute  system  of  meas- 
urement, viz.  :  The  (Centimetre)  the  unit  of  length.  The 
(Gramme)  the  unit  of  mass.  The  (Second)  the  unit  of  time. 


110  AKMATUKE   AND   FIELD-MAGNET  WINDING. 


SIGNIFICATIONS 

OF    SIGNS  USED    IN    CALCULATIONS. 

=  signifies  equality,  thus  5-1-2=7. 

-f-  signifies  addition,  thus  3-)- 2=5. 

—  signifies  substraction,  thus  8 — 6=2. 

X  signifies  multiplication,  thus  5X3—15- 

-f-  signifies  division,  thus  i8-f-3=6. 

:  : :  :  signifies  proportion,  thus  2  is  to  3 — . 

y    signifies  square  root  thus  \  =4. 
•ty  signifies  cube  root,  thus  -3/64=4. 

32  signifies  3  is  to  be  squared  32=9- 

33  signifies  3  is  to  be  cubed  33=27. 


ARMATUKE    AND    FIELD-MAGNET   WINDING. 


Ill 


APPENDEX  B. 

USEFUL  TABLES. 
TABLE     OF     ELECTRICAL      UNITS. 


UNIT  OF 

NAME 

DERIVATION. 

Dimen- 
sions in 
C.  G.  S. 
Units. 

Electromotive 
force  

Resistance  

Volt  
Ohm  .    . 

Ampere  X  Ohm.   . 
Volt  ~=~  Ampere.  .  .  . 

I08 
I09 

Current  . 

Ampere 

Volt  •  Ohm 

I01 

Quantity..  . 

Coulomb 

Ampere  X  Second 

I01 

Capacity  

Farad  

Coulomb  —  Volt.  .  . 

I09 

112 


ARMATURE    AND  'FIELD-MAGNET   WINDING. 


TABLE    SHOWING   THE    DIFFERENCE     BETWEEN  WIRE   GAUGES. 


New 

Brown  & 

No. 

British.     I 

London. 

Stubs'.      , 

Sharpens. 

0000  .... 

.400  .... 

.454  .... 

.454  .... 

.460 

000  .... 

.372  .... 

.425  .... 

.425  .... 

.40964 

00  .... 

.348  .... 

.380.  .  .  . 

.380  .... 

.36480 

0  

.324  .... 

.340  .... 

.340  .... 

.32495 

1  

.300  .... 

.300  .... 

.300  .... 

.28930 

2  

.276  .... 

.284  .... 

.284  .... 

.25763 

3  

.252  .... 

.259  .... 

.259  .... 

.22942 

4  

.232  .... 

.238  .... 

.238  .... 

.20431 

5  

.212  .... 

.220  .... 

.220  .... 

.18194 

6  

.193  .... 

.203  .... 

.203  .... 

.16202 

7  

.176  .... 

.180  .... 

.180  .... 

.14428 

8  

.160  .... 

.165  .... 

.165  .... 

.12849 

9  

.144  .... 

.148  .... 

.148  .... 

.11443 

10  

.128  .... 

.134  .... 

.134.  .  .  . 

.10189 

11 

116 

.120    .  . 

.120  .... 

.09074 

12  

.10J  .... 

.109  .... 

.109  .... 

.(,8081 

13  

.092  .... 

.095  .... 

.095  ..,. 

.07196 

14  

.080  .... 

.083  .... 

.083  .... 

.06408 

15  .. 

.072  .... 

.072  .... 

.072  .... 

.05706 

16  

.064  .... 

.065  .... 

.065  .... 

.05082 

17  .   .  .  . 

.056  .... 

.058  .... 

.058  .... 

.04525 

18  

.048  .... 

.049  .... 

.049  .... 

.04030 

i9  

.040  .... 

.040  .... 

.042  .... 

.03589 

20  

.030  .... 

.035  .   .  . 

.035  .... 

.03196 

21  

.032  .... 

.0315  .  .  . 

.032  .... 

.02846 

22 

.028    .  . 

.0295  .  .  . 

.028  .... 

025347 

23  

.024  .... 

.027  .... 

.025  .... 

.022571 

24  

.022  .... 

.02'>  .... 

.022  .... 

.0201 

25  

.020  .... 

.023  .... 

.023  .... 

.0179 

26 

018 

.0105  .  .  . 

.018  .... 

.01594 

27 

.0164  .  .  . 

.01875  .  .  . 

.016  .... 

.014195 

28  

.0148  .  .  . 

.0165  .  .  . 

.014  .... 

.012641 

29  

.0136  .  .  . 

.0155  .  .  . 

.013  .... 

.011257 

30  

.0124  .  .  . 

.01375  .  .  . 

.012  .... 

.010025 

31   .  . 

.0116  .  .  . 

.01225  .  .  . 

.010  .... 

.008928 

09 

O£i  

.0108  .  .  . 

.01125  .  .  . 

.009  .... 

.00795 

33  

.0100  .  .  . 

.01025  . 

.008  .... 

.00708 

34  

.0092  .  .  . 

.009)  .  .  . 

.007  .... 

.0063 

35  

.0084  .  .  . 

.009  .... 

.005  .... 

.00561 

36. 

.0075  . 

.0075  . 

.004. 

.005 

AKMATURK    AND   FIELD-MAGNET   WINDING. 


113 


Table  of  Different  Ganges,  with  their  Diameters  and  Areas  in  Mils. 


1 

STANDARD 

i 

AMERICAN 

a 

RMINGHA 

M. 

No   of 
Gauge. 

Diameter 
in  Mils. 

Area  In 
CM=d« 

No.  of 
Gauge. 

Diameter 
in  Mils. 

Area  in 
CM=d2 

No.  of 
Gauge. 

Diameter 
in  Mils 

Area  in 
CM=d« 

7-0 

500 

250000 

6-0 

464 

21o296 

4-0 

4600 

211600 

4-0 

454 

206116 

6-0 

A    J32 

3-0 

425 

180625 

4-0 

160000 

3-0 

4096 

167805 

3-0      j 

rJ   372 

138384 

2-0 

3648 

133079 

2-0 

380 

144400 

3-0    J 

'/    348 

121104 

0 

340 

1156(10 

'      324 

104976 

0 

3249 

105592 

IM 

300 
276 

90000 
76176 

2893 

83694 

300 
384 

90000 
80656 

JT 

262 

63504 

2576 

66373 

259 

67081 

9 

232 

6S824 

2294 

62634 

238 

312 

44944 

220 

48400 

6 

7 

192 

176 

36864 
30976 

2043 
1819 

41742 
8Si02 

HI 
180 

41309 
32400 

8 

160 

26600 

162 

26244 

165 

37225 

9 

141 

20736 

1443 

20822 

148 

21904 

10 

128 

16384 

1285 

16613 

1 

134 

179T6 

Table  of  Different  Gauges,  with  their  Diameters  and  Areas  in  Mils, 


STANDARD 

AMERICAN. 

BIRMINGHAM 

No.  of 

Diameter 

Area  In 

No.  of 

Diameter 

Area  In 

NO    Of 

Diameter 

Area  tn 

Gauge. 

111    MllB. 

0  M=d* 

Gauge. 

lu  Mils. 

CM=d* 

Gauge. 

in  Mils. 

CM=dt 

11 

llrt 

13456 

9 

11*  \ 

13110 

11 

120 

14400 

12 

10816 

10 

1019 

10381 

12 

109 

11881 

13 

IN 

MM 

11 

01107 

8*26 

13 

095 

90% 

on 

6400 

12 

0808 

R.V28 

14 

083 

6889 

15 

072 

8181 

13 

073 

5184 

16 

072 

5184 

16 

061 

4096 

14 

UMI 

4110 

16 

065 

4229 

17 

056 

S1S6 

15 

0571 

3260 

17 

(168 

3364 

18 

048 

23U4 

16 

0508 

2581 

18 

049 

2401 

17 

.0*52 

2044 

19 

042 

1764 

19 

040 

1600 

18 

0403 

1624 

90 

036 

1296 

19 

0359 

1253 

20 

035 

1325 

i 

032 
028 

1024 
784 

20 
21 

032 
0286 

1024 

M 

i 

032 
028 

1024 
784 

93 

024 

576 

93 

0253 

626 

33 

025 

635 

84 
96 

023 

5 

484 
400 

93 
34 

0226 
0301 

MO 
404 

033 
030 

484 
400 

• 

•IS 

M4 

• 

•179 

330 

5 

U18 

Stt 

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practice  upon  this  subject.  It  also  contains  working 
directions  for  Winding  Dynamos  and  Motors,  with  addi- 
tional Descriptions  of  some  of  the  apparatus  made  by  the 
several  leading  Electrical  Companies  in  the  U.  S. 


•CONTENTS. 


INTRODUCTION. 

CHAPTER  1. — The  Armature  in  Theory. 

CHAPTER  2.— Forms  of  Armatures. 

CHAPTER  3. — Drum  Winding. 

CHAPTER  4. — Field  Winding. 

CHAPTER  5.— Field  Formulae. 

CHAPTER  6. — General  Methods  of  Winding. 

CHAPTER  7.— Field  Winding— concluded. 

CHAPTER  8. — Dynamos. 

CHAPTER  9. — Motors. 


PRICE,  S1.5O,  Postpaid. 

BUBIER  PUBLISHING  COMPANY, 

LYNN,    -     MASS. 


A  PRACTICAL  BOOK! 

PRICE,   25   CENTS. 

NOW    READY. 

"How  to  JMe  Electric  Bat- 
teries at  Home." 


By     EDWARD 

ILLUSTRATED. 


This  little  volume  will  contain  just  the  information  needed 
to  make  Simple,  yet  Practical  Electric  Batteries  (both  open 
and  closed  circuit),  by  which  you  can  run  Electric  Motors,  In- 
candescent Lamps,  or  operate  Telegraph  Lines,  ring  Electric 
Bells,  etc.  It  will  inform  you  of  the  necessary  articles  required 
for  their  manufacture,  giving  price  of  the  same  as  near  as  pos- 
sible— the  expense  of  making  such  batteries  being  so  small 
that  any  schoolboy  may  afford  them.  Most  of  the  articles  re- 
quired can  be  obtained  at  home  or  at  the  neighboring  drug 
store. 

YOU  CANNOT  AFFORD  TO  BE  WITHOUT  THIS  BOOK. 

Sent  Postpaid  on  Receipt  of  Price. 

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f  Everybody's   Hand-Book   of    Electricity. 

ZHITrTnR      HF   1  How   ^°   Make    Electric    Batteries    at  Home. 
JrlU  1   llUlv     UT     |  Experimental    Electricity. 

(  Dynamos  and  Electric   Motors. 

"Electricity  and  its  Recent  Applications." 

Containing  nearly  350  pages  and  about  250  Illus. 

This  work  is  printed  on  extra  fine  heavy  paper,  is  bound  in  a, 
neat  cloth  binding,  and  lettered  in  gold.    It  is  particu- 
larly adapted  to  the  use  of  Students. 

CONXKNTS. 


CHAP.    1. — Electricity  and  Magnetism. 

CHAP.    2. — Voltaic  Batteries. 

CHAP.    3. — Dynamos,  and  How  to  Build  One. 

CHAP.    4. — The  Electric  Arc,  and  The  Arc  Lamp. 

CHAP.    5. — Electric  Motors  and  How  to  Build  One. 

CHAP.    6.— Field  Magnets. 

CHAP.    7. — Armatures. 

CHAP.    8.— The  Telegraph  and  Telephone. 

CHAP.    9.— Electric  Bells.— How  Made,  How  Used. 

CHAP.  10. — How  to  Make  an  Induction  Coil. 

CHAP.  11. — The  Incandescent  Lamp. 

CHAP.  12. — Electrical  Mining  Apparatus. 

CHAP.  13.— The  Modern  Electric  Railway. 

CHAP.  14.— Electric  Welding. 

CHAP.  15. — Some  Miscellaneous    Electric    Inventions    of    the 

Present  Day. 

CHAP.  16. — Electro-Plating. 
CHAP.  17.— Electric  Gas  Lighting  Apparatus. 
CHAP.  18. — Electrical  Measurement. 
CHAP.  19.— Resistance  and  Weight  Table  for  Cotton  and  Silk 

Covered  and  Bare  Copper  Wire. 
CHAP.  20.— Illustrated    Dictionary    of   Electrical    Terms    and 

Phrases. 


PRICE         $2.OO. 


BUSIER  PUBLISHING  CO.,    Lynn,   Mass. 


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APR    Itf  1935 

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= 

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MP,V       1_13£S..&J7. 

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JAN  2  fe  '66- 

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T  TI  01     i  nn«»  Q  to  A 

UNIVERSITY  OF  CALIFORNIA  LIBRARY 


